Distribution of foraminifera and sub-millennial scale paleoclimatic reconstruction from marine
sediments off southwest coast o f India
Thesis submitted To the
Department of Earth Sciences, Goa University, Goa
for the award of degree of
5 G 0
DOCTOR OF PHILOSOPHY
Dinesh K um ar N aik
Micropaleontology Laboratory National Institute o f Oceanography,
Dona Paula - 403 004, Goa, India.
20 17
T- 3
Declaration
As required under the university ordinance OB.9A.12, I hereby state that the present
reconstruction from marine sediments off southwest coast of India” is my original contribution and the same has not been submitted on any previous occasion. To the best of my knowledge, the present study is the first comprehensive work of its kind from the area mentioned.
Literature related to the problem investigated has been cited. Due acknowledgements have been made wherever facilities and suggestions have been availed of.
thesis entitled “Distribution of foraminifera and sub-millennial scale paleoclimatic
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Dinesh Kumar Naik
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CSIR - national institute o f oceanography
( Council o f Scientific & Industrial R esearch )
Date: - 0 & ' 2 . ° / ?
Certificate
As required under the university ordinance OB.9A.4 (vi and viii), we certify that the thesis entitled “Distribution of foraminifera and sub-millennial scale paleoclimatic reconstruction from marine sediments off southwest coast o f India”, submitted by Mr.
Dinesh Kumar Naik for the award of the degree of Doctor of Philosophy in Earth Science is based on original studies carried out by him under our supervision. The thesis or any part thereof has not been previously submitted for any other degree or diploma in any university or institution.
(R. Nigam) Supervisor
Consultant and Former Chief Scientist
(R. Saraswat) Co-Supervisor Senior Scientist
'trawl, *irar 403 004 ^trct
d o n a PAULA, GOA - 403 004, India
P r e fa c e
Over the past few years, Climate change and its impact on human and environmental systems became an important topic of research both nationally and internationally. The ongoing change in environmental conditions apparently due to increase in greenhouse gases, became one of the biggest challenges faced by our planet. The study of long-term climate changes can help to find out the cause of climatic variations and possible influence of anthropogenic activities. The past climate reconstruction is also very essential for future climate projection. As the past instrumental climatic record is very short (not beyond the last -100-150 years), proxies or indirect methods are used to infer past climate variations. These paleoclimatic proxies are developed by studying their natural characteristics in the present environmental conditions. Among different proxies, oceanic proxies are considered to be one o f the vital proxies for paleoclimatic studies as they can provide data of longer time scale and are stored and preserved in a relatively undisturbed environment. The present study deals with reconstruction of past climate and development refinement of new oceanic paleoclimatic proxies using the microfossil foraminifera from southestem Arabian Sea. The entire work is presented in eight chapters.
Chapter one comprises general introduction, scope of the study in present scenario, importance of microfossils and foraminifera in paleoclimatic and paleoceanographic studies.
Chapter two comprises a detailed literature survey o f foraminiferal work from the study area. The survey gives the details of all the foraminiferal (fossil) studies carried out till date from the southeastern Arabian Sea and a few adjacent regions. The different foraminiferal studies have been categorized according to their themes and summarized under their respective headings. Literature survey on foraminiferal distribution from eastern Arabian Sea demonstrate that the previous studies are confined to near shore to very shallow regions with limited areal extents. Taking all these aspects in to consideration, the southeastern Arabian Sea from off Karwar to off Cochin within a depth
m
range of 24 m to 3150 m was selected for the present investigation with the following objectives.
• To catalogue and illustrate the distribution of foraminifera from both surface and sub-surface sediment samples.
• To study the relationship between ecological parameters and foraminiferal distribution in the study area.
• To apply this relationship to the down core distribution of foraminifera in the study area.
• To reconstruct past climate and the delineation of major climatic events of the proposed study area by foraminiferal proxies.
Chapter three provides the detailed account of study area and its physiographic settings. The study area covers the region off southern west coast of India from off Karwar to off Cochin. The physiographic setting includes bathymetry, sea surface temperature, sea surface salinity, ocean currents, primary productivity, different oceanographic phenomenon, bottom water physiochemical parameters (temperature, salinity, dissolved oxygen, nutrients), water column depth profile of sea water temperature and salinity o f the study area.
Chapter four deals with the materials and methodology used for the study. A total of 434 sediment samples (both surface and sub-surface) were used. The samples were collected onboard ORV Sagar Kanya (SK 237). Out of the total samples, 47 are surface and 387 are sub-surface samples. The surface samples are the top 0-1 cm of the spade cores collected along five latitudinal transects. The sub-surface samples are from two gravity cores, viz. GC04 and GC09. The gravity core GC04 (having 287 samples) was collected (10°58.65’ N, 74°59.96’ E) from 1247 m water depth and GC09 (having 100 samples) was collected (12°00.59’ N, 70°52.20’ E) from 3001 m water depth. The sediments were processed following the standard procedure and wet sieved through 63 pm sieve using a very low shower with low water pressure. The plus 63 pm fraction was transferred into small beakers and dried overnight. The dried coarse fraction was weighed and stored in plastic vials. For total carbon (TC) and total nitrogen (TN) analysis, a small
amount of dry sediment sample (approximately 2-3 g) was powdered by using an agate mortar and pestle. Approximately 10-20 mg o f the powdered sample was placed into the C-N analyzer following the standard procedure. The total inorganic carbon (TIC) was analyzed by using Coulometer. For TIC analysis, a small amount (10-20 mg) of powdered dry sediment was placed in the acidification module of coulometer. The total organic carbon (Corg) was calculated by subtracting total inorganic carbon from total carbon. The calcium carbonate percentage (%CaCC>3) was calculated by subtracting total inorganic carbon from total carbon.
The core SK237 GC04 spans the last ~32 kyr BP, and the core top shows essentially modem conditions (age 115 yr BP). The sediment accumulation rate o f this core averages 9.1 cm/kyr and the average sample resolution shows —110 yr. In the core SK237 GC09 top 100 cm covers a time span of ~45 kyr BP, and the sediment accumulation rate averages 2.4 cm/kyr. The average sample resolution of the core shows
—418 yr.
The stable isotopic ratio of surface dwelling planktic foraminifera, Globigerinoides ruber were measured at Alfred Wegener Institute of Polar and Marine Research (Bremerhaven) using a Finnigan MAT 251 isotope ratio gas mass spectrometer coupled to an automatic carbonate preparation device (Kiel IV) and calibrated via NBS 19 to the PDB scale. Elemental analysis on G. ruber was carried out by using a Thermo Finnigan Element2 sector field ICP-MS following the isotope dilution/intemal standard method.
Chapter five includes the systematic description and illustration of all the specimens identified from the study area. The species level identification follows Ellis and Messina Catalogue, (2007) and the generic positions have been decided following the treatise (Loeblich and Tappan; 1988). A total of 293 species, belonging to 104 genera, 49 family, 28 superfamily and 6 suborder o f the order Foraminiferida have been reported.
Out of the total 293 species, 24 species are planktic and the rest 269 are benthic.
Chapter six deals with surface distribution of foraminifera and their relationship with different environmental parameters. Out o f the total genera, only 25 significant ones were selected by using the application principal component analysis (PCA) in the programe “STATISTICA”. The 25 significant genera were then run in the application
“CANOCO” applying the method canonical correspondence analysis (CCA) to find out their relationship with different environmental parameters o f the study region. The analysis shows that out of nine environmental variables nutrients, bottom water dissolved oxygen and coarse fraction are statistically significant.
Q-mode cluster analysis of all the stations groups similar stations based on foraminiferal assemblages. The analysis resulted in six significant groups (Group-I to VI) and the results are presented in the form o f dendrogram. The grouping of stations follow the bathymetric pattern of the study area where Group-I is represented by deep water stations, Group-II represents intermediate water stations, Group-Ill represents shallow water stations and the rest Group-IV, V, VI comprises only 2 stations each in the shallow to very shallow water. Each group is characterized by a certain foraminiferal assemblage having different contribution percentage for each genus.
Chapter seven includes paleoclimatic reconstruction from the southeastern Arabian Sea. All the subsurface samples from the cores SK237 GC04 and GC09 were subjected to both faunal and geochemical analysis. Paleoclimatic reconstruction from the study area includes quantitative estimation of sea surface temperature and monsoon changes during the last deglaciation, reconstruction of last glacial-interglacial productivity changes, timing, causes and consequences o f mid-Holocene climate transition, Indo-Pacific warm pool (IPWP) teleconnection between Indian Ocean and Pacific Ocean. I report that the SST at the Last Glacial Maximum was 2.7±0.5 °C colder than pre-industrial SST. Deglacial warming started at 18.6 kyr BP, within error of the onset of warming at other tropical sites as well as in Antarctica and the Southern Ocean and either coeval with or up to 1 kyr before the atmospheric CO2 rise. The 818Osw and the Ba/Ca record, a measure of Indian sub-continent riverine runoff, indicate that the last ice age termination was marked by a prominent weak monsoon interval interrupted by an intense monsoon phase. I further report that that although the productivity was higher in
the eastern Arabian Sea during the larger part of the last glacial interval, the overall resultant carbon sequestration was confined only to a restricted zone and not large enough to substantially alter atmospheric C 0 2. The work also suggests that the global 813C minimum event during the last deglaciation was associated with the weak monsoon interval during HS-1 and a drop in productivity in tropical regions. A major shift in proxies during the mid-Holocene (6.8 to 6.2 ka) and its comparison with previously published records, shows a regional mid-Holocene climate transition (MHCT). The MHCT is also evident in the terrestrial records. The widespread nature of the MHCT event in both the marine and terrestrial records suggests that the mid-Holocene transition affected the entire Asia and adjoining seas. The MHCT coincides with decreasing low- latitude summer insolation, perturbations in total solar intensity and an increase in atmospheric C 02. The very well correspondence of centennial scale SST and 518Osea water (salinity proxy) record from the southeastern Arabian Sea with that of western equatorial pacific suggests that Indo-Pacific warm pool is not only a modem oceanic phenomenon but exists since last glacial period. The onset of last deglacial warming in the southeastern Arabian Sea preceded the western equatorial Pacific Ocean by 0.9 kyr. The average Holocene SST of western equatorial Pacific Ocean is 2.52 °C higher than that of SE Arabian Sea.
The interferences are mentioned in Chapter eight. This chapter is followed by the references cited in the text. The foraminiferal plates described in chapter five are placed after the references. The list of all the species in alphabetical order is provided in Annexure I.
VII
Contents
Page No.
Declaration i
Certificate ii
Preface iii
Contents viii
List of Figures xii
List of Tables xix
Acknowledgement xx
Chapter 1 Introduction 1
Chapter 2 Previous Studies 4
2.1 Introduction 4
2.1.1 Studies on distribution of foraminifera 4 2.1.2 Cluster analysis and ecological studies on 6
benthic foraminifera
2.1.3 New species and first time reported species 7 2.1.4 Studies on morphological aspects o f foraminifera 7 2.1.5 Isotopic and elemental studies 8 2.1.6 Studies on sediment accumulation rate 9 2.1.7 Studies on paleomonsoon reconstruction 9 2.1.8 Studies on sea surface salinity 11 2.1.9 Studies on paleo sea surface temperature 12
reconstruction
2.1.10 Studies on primary productivity 13 2.1.11 Studies on carbon content of the sediments 14 2.1.12 Studies on paleo-sea level changes 15 2.1.13 Foraminiferal studies on oxygen minimum zone 15
(OMZ)
2.1.14 Pollution monitoring and environmental studies 16
2.2 Objectives 16
Chapter 3 Study Area and Physiographic Setting 18
3.1 Study Area 18
3.2 Physiographic Setting 19
3.2.1 Ocean Currents 19
3.2.2 Primary productivity 20
3.2.3 Arabian Sea mini warm pool 21
3.2.4 Bottom water physiochemical parameters 22
3.2.5 Sea surface salinity 23
3.2.6 Sea surface temperature (SST) 26 3.3 Water column profiles of seawater temperature and 26
salinity at core locations
Chapter 4 Materials and Methodology 30
4.1 Sample collection 30
4.2 Sub-sampling of sediment core 33
4.3 Processing of sediment samples 33
4.4 Picking of foraminifera 34
4.5 Total Carbon and Total Nitrogen analysis 34
4.6 Total Inorganic/Carbon analysis 34
4.7 Morpho-groups 35
4.8 Identification 35
4.9 Foraminiferal Elemental Analysis 35
4.10 Foraminiferal Isotopic Analysis 36
4.11 Accelerator Mass Spectrometer (AMS) Radiocarbon 36 dating
4.11.1 Chronology of SK237 GC04 37
4.11.2 Chronology o f SK237 GC09 39
Chapter 5 Systematic Description of Foraminifera 40
5.1 Introduction 40
5.2 Systematic Description format 41
5.3 Salient Observations 42
5.4 Abundance of taxa under Suborders 42
5.5 Systematic Taxonomy 50
5.6 Comparison with previous reports 124
Chapter 6 Surface Distribution of Foraminifera 125 6.1 Distribution of total carbon (TC), total organic carbon 125
(Corg) and total inorganic carbon (TIC)
6.2 Foraminiferal distribution in response to environmental 126 variables
6.2.1 Genera having significant relationship with 128 bottom water nutrients
6.2.2 Genera showing significant relationship with 130 bottom water dissolved oxygen
6.2.3 Abundance of coarse fraction and benthic 132 foraminifera
6.2.4 Genera showing significant relationship with 133 depth
6.2.5 Genera showing significant relationship with 135 bottom water salinity
6.3 6.2.6 Genera showing significant relationship with 137 bottom water temperature
Generic distribution o f foraminifera in response to 138 carbon content
6.3.1 Generic distribution in response to total inorganic 138 carbon (TIC)
6.3.2 Generic distribution in response to total organic 140
6.4 carbon (Corg)
6.5 6.3.3 Generic distribution in response to total carbon 140
6.6 (TC)
Grouping of stations based on different environmental 142 variables
Cluster analysis 142
Inferences 146
Chapter 7 Paleoclimate Reconstruction 149
7.1 Deglaciation in the tropical Indian Ocean 149
7.1.1 Introduction 149
7.1.2 Results and Discussion 151
7.1.2.1 Description of SST record o f the core 151 SK237 GC04
7.1.2.2 Comparison o f the SK237 GC04 SST 154 record with atmospheric CO2 rise
7.1.2.3 Factors other than CO2 that might have 155 driven SK237 GC04 SST
7.1.2.4 Deglacial Changes in the Indian 158 Monsoon and the link to the North Atlantic
7.1.3 Conclusions 163
7.2 Last glacial-interglacial productivity and associated 164 changes
7.2.1 Introduction 164
7.2.2 Results 166
7.2.3 Discussion 169
7.2.3.1 Last Glacial Interval 169
1 .2 3 2 The Deglaciation 174
7.2.3.3 Early Holocene 175
7.2.3.4 Late Holocene 176
7.2.3.5 Regional Productivity Changes 177 7.2.3.6 Global Teleconnections and 179
Implications
7.2.4 Conclusions 181
7.3 Timing, cause and consequences of mid-Holocene 182 climate transition
7.3.1 Introduction 182
7.3.2 Results 184
7.3.3 Discussion 186
7.3.3.1 Comparison with global records 191 7.3.3.2 Causes and consequences 191
7.3.4 Conclusions 194
7.4 Teleconnection between Indian Ocean and Pacific 194 Ocean
7.4.1 Introduction 194
7.4.3 Conclusions 199
Chapter 8 Inferences 201
References 206
Explanation of Plates 242
Annexure I List of species (in alphabetical order) reported, along with their plate, figure and text details.
266
Annexure II Publications 273
List o f F ig u r es
Figure No.
Figure 3.1 Figure 3.2
Figure 3.3
Figure 3.4 Figure 3.5
Figure 3.6
Figure 3.7
Figure 3.8 Figure 3.9
Figure 3.10
Figure Title The study area
Water circulation during (A) Southwest monsoon, (B) Northeast monsoon (modified after Schott and McCreary, 2001); The black elliptical circle highlights the study region where a large difference in sea surface salinity can be observed during (C) Southwest monsoon and (D) Northeast monsoon. (Source: Levitus Climatology)
Chlorophyll a concentration (mg/m3) of Arabian Sea (A) Annual (B) Pre southwest monsoon (C) Northeast monsoon (C) Southwest monsoon. (Source: Giovanni webpage (http ://gdata 1. sci. gsfc.nasa. go v/daac-
bin/G3/gui.cgi?instance_id=ocean_month))
Sea surface temperature in the month of April showing Indo Pacific Warm Pool. (Source: Levitus Climatology)
Annual average bottom water isopleths of (A) Temperature, (B) Salinity, (C) Dissolved Oxygen and (D) Nutrients in the study area. (Source: World Ocean Atlas 2013)
Sea surface salinity in the study area during (A) Winter, (B) Spring, (C) Summer and (D) Autumn season. Figure (E) shows the annual average sea surface salinity in the study area. (Source: Levitus Climatology)
Sea surface temperature in the study area during, (A) Winter, (B) Spring, (C) Summer and (D) Autumn season. Figure (E) shows the annual average sea surface temperature in the study area. (Source: Levitus Climatology)
Annual seawater temperature and salinity at the two core locations. (Source: Levitus Climatology)
Seasonal seawater temperature at the two core locations during, Winter (Red), Spring (Blue), Summer (Pink) and Autumn (Green) seasons. (Source: Levitus Climatology) Seasonal seawater salinity at the two core locations during, Winter (Red), Spring (Blue), Summer (Pink) and Autumn (Green) seasons. (Source: Levitus Climatology)
Page No.
18 19
20
21
22
24
25
27
28
28
31
38
39
43 44 126 127
129
130
131
xiii Both the surface and subsurface samples used for the present
work are plotted. Dotted lines are depth contours. Black circles filled with light grey color, are spade core locations.
Black square shows the location o f gravity core SK237 GC04 and black triangle is the location of gravity core SK237 GC09 Age model of GC04 core, developed from AMS radiocarbon dates (black symbols). The dates are plotted against the depth interval in the core and were used as tie points. Sediment accumulation rates between tie points are shown in between Age model of SK237 GC09, established from AMS radiocarbon dates (black symbols). The dates are plotted against the depth interval in the core and were used as tie points. Sediment accumulation rates between tie points are shown in between
Relative percentage of various taxa under suborders
Relative percentage of species under various superfamilies Surface distribution of total carbon (A), organic carbon (B) and inorganic carbon (C) in the southeastern Arabian Sea Canonical correspond analysis (CCA) o f foraminiferal abundance with different environmental parameters in the southeastern Arabian Sea. Environmental variables such as bottom water nutrients (BW Nutrient) (nitrate, phosphate and silicate), bottom water dissolved oxygen (BW DO), coarse fraction per gram sediment (CF), water column depth (Depth), bottom water salinity (BW Sal), total inorganic carbon (TIC), bottom water temperature (BW Temp), total carbon (TC) and total organic carbon (Corg) are indicated by red arrows. All 25 genus and one morpho-group are indicated by triangles. Genus abbreviations are listed in Table 6.2
Surface distribution of genus Epistominella (A), Bottom water nutrients isopleths (B), genus Osangularia (C) and genus Quinqueloculina (D) in the southeastern Arabian Sea Surface distribution of genus Bulimina (A), Bottom water dissolved oxygen isopleths (B), Cassidulina (C) and genus Hofkeruva (D) in the southeastern Arabian Sea
Surface distribution of coarse fraction (A), abundance of benthic foraminifera (B), Pseudononion (C) and genus Nonionella (D) in the southeastern Arabian Sea
133
136
137
138
139
140 141
143
144 151 Surface distribution of genus Stainforthia (A), Parafissurina
(B), Bolivina (C), angular asymmetrical benthic foraminifera (AABF) (D) and rounded symmetrical benthic foraminifera (RSBF) (E) in the southeastern Arabian Sea
Surface distribution of genus Bolivina (A), bottom water salinity isopleths (B), angular asymmetrical benthic foraminifera (AABF) (C) and genus Neouvigerina (D) in the southeastern Arabian Sea
Surface distribution of genus Stainforthia (A), Bottom water salinity isopleths (B), Parafissurina (C) and genus Lagena (D) in the southeastern Arabian Sea
Surface distribution of genus Cancris (A), Bottom water temperature isopleths (B), Cibicicoides (C) and genus Osangularia (D) in the southeastern Arabian Sea
Surface distribution of genus Gallitellia (A), total inorganic carbon (B), Globocassidulina (C), Hofkeruva (D), organic carbon (E) and genus Cassidulina (F) in the southeastern Arabian Sea
Surface distribution of genus Nonionella (A), total carbon (B) and genus Evolutononion (C) in the southeastern Arabian Sea Canonical correspondence analysis (CCA) of foraminiferal abundance at all surface stations with associated environmental variables in the southeastern Arabian Sea (Station biplot with environmental variables). Environmental variables, namely bottom water nutrients (BW Nutrient), bottom water dissolved oxygen (BW DO), coarse fraction per gram sediment (CF), water column depth (Depth), bottom water salinity (BW Sal), total inorganic carbon (TIC), bottom water temperature (BW Temp), total carbon (TC) and total organic carbon (Corg) are indicated by red arrows. Stations are indicated by green filled circles
Cluster analysis dendrogram for all surface stations based on benthic foraminiferal assemblages in the southeastern Arabian Sea
Grouping of surface samples based on cluster analysis of generic abundance
Variation in G. ruber Mg/Ca (SST), Ba/Ca, b180 and b180 of seawater in core SK237-GC04 (10°58.65' N, 74°59.96' E,
Figure 7.1.2
Figure 7.1.3
Figure 7.1.4
Figure 7.2.1
1247 m water depth). The intervals marking major changes in trace metal and stable isotopic ratio have been dated by AMS radiocarbon and are shown by inverted filled triangles. The average resolution of the data is 110 yr. Ba/Ca data is not shown for the samples younger than 5.4 kyr because the data is likely overprinted by early diagenesis. Two Ba/Ca points are shown as outliers. The onset of deglaciation in Mg/Ca occurs at 18.6 (18.8-18.1) kyr, in 5180 at 16.4 (16.7-15.3) kyr and in Ba/Ca at 15.1(15.6-14.5) kyr
Comparison of the core SK237 GC04 SST record with low 153 latitude insolation changes in mid-July at 10°N (Lasker et al.,
2004) and the Greenland NGRIP (NGRIP members, 2004) and Antarctic EDC (Jouzel and Masson-Delmotte, 2008) proxy temperature records. The red vertical bar shows the overall magnitude of the error associated with SK 237 GC04 SST
Comparison of Termination I warming in the southeastern 155 Arabian Sea with the average northern and southern
hemispheric temperature records (Shakun et al., 2012). The deglacial CO2 changes in the Antarctic region (Monnin et al., 2001) are plotted to compare the timing of deglacial warming in the tropics and changes in the atmospheric concentration of CO2. The shaded vertical bar marks the mid-termination SST plateau in the core SK 237 GC04, which occurs between 15.7 (16.2-14.9) and 13.2 (13.9-12.0) kyr BP. The minimum that follows the SST plateau, at 12.9 (13.6-11.7) kyr BP, is coeval with similar features in other records and likely occurred during the Younger Dry as stadial
Comparison of 8lsO of seawater of core SK237 GC04 and 159 Ba/Ca (surface runoff) records with 815N from the eastern
Arabian Sea (RC27-14) (Altabet et al., 2002), the Hulu/Dongge Cave 5180 record from China (Cheng et al., 2009), and the Antarctic (EDC) methane record (Loulerge et al., 2008). The weak monsoon intervals (WMI) inferred from the Hulu Cave record have correlatives in all o f the records shown
Location of core SK237 GC04 is marked with a blue 167 rectangle, whereas other cores discussed in this section are
plotted as filled circles: 1- MD76-131, Ivanochko, 2004; 2- SK117 GC8, Banakar et al., 2005; 3- SK17, Singh et al., 2006; 4- 3104G, Agnihotri et al., 2003; 5- SK126 GC39, Kessarkar et al., 2010; 6- AAS62 GC01, Kessarkar et al., 2013; 8- AAS38 GC5, 9- AAS38 GC4, Narayana et al., 2009;
xv
Figure 7.2.2
Figure 7.2.3
Figure 7.2.4
Figure 7.2.5
Figure 7.3.1
10- SK20-185, Sarkar et a l, 1993; 11- SK129 CR05, Guptha et al., 2005; 12- SK126 GC16, Anil Kumar et ah, 2005; 13- MD77-191, Sirocko, 2002; 14- 3101G, Agnihotri et al., 2003;
15- MD 900963, Cayre et al., 1999. The background is the bathymetry (plotted with Ocean Data View) with the scale on the right side of the map
A. Relative abundance o f planktic foraminifer G. bulloides,; 170 B. %Corg; C. CaC03 weight percentage; D. TC; E. Percentage
of coarse fraction (CF) (>63 pm); F. Abundance of all planktic foraminifera (PF) per gram dry sediment; G. Relative abundance of AABF; H. &]3Cruber', and I. Ice-volume corrected
§180 (518Osw-ivc)v The grey shaded bar is the last glacial maximum and younger Dry as interval
A compilation of CaC03 (%) changes during the last 35 ka in 178 different cores collected from the eastern Arabian Sea. The
cores are plotted with the northernmost core on the top and the southernmost on the bottom. The water depth o f the core is given in parenthesis, next to each record. For details of each core, refer to Figure 7.2.1, and Table 7.2.1
A compilation of %C0ig changes during the last 35 ka in the 179 different cores collected from the southeastern Arabian Sea.
The cores are plotted with the northernmost core on the top and the southernmost on the bottom. The water depth o f the core is given in parenthesis, next to each record. For details of the core, refer to Figure 7.2.1 and Table 7.2.1
All productivity/monsoon proxy indicators analyzed in the 180 core SK237 GC04, along with the SST (from Saraswat et al.,
2013): A- %CaC03; B- %Corg; C- Relative abundance of G.
bulloides-, D- 813C; E- 8,8Osw.ivC. The SST change during the same interval is also plotted (F) (Saraswat et al., 2013). The vertical gray shaded region indicates Heinrich Stadials marked as HS-1 and HS-2. The %Corgas well as S13C in the SEAS decreases during high latitude Heinrich Stadials. The HS are also marked by increase in 518Osw.iVC. A similar consistent response is, however, not observed in %G.
bulloides based productivity changes
The core location in the southeastern Arabian Sea is marked 183 by an open black rectangle. Other cores discussed in the text
are marked by filled black star (1. SK17, Anand et al., 2008;
2. 63KA-41KL, Staubwasser et al., 2003; 3. RC27-23, Altabet et al., 2002). The template is surface primary productivity
southwest monsoon season (June-July-August-September) (Acker and Leptoukh, 2007)
Figure 7.3.2 Changes in faunal and geochemical parameters in core SK237 GC04. A. Mg/Ca ratio in G. ruber, a proxy for seawater temperature; B. 5180ruber which has been used to determine
18 • •
5 Osw-ivc? a proxy for local precipitation-evaporation changes at the core site; C. CaCCL weight percentage; D. Organic carbon weight percentage (Corg); E. Relative abundance of planktic foraminifer G. bulloides, a proxy for primary productivity; F. Percentage o f coarse fraction (CF) (>63 pm);
G. Abundance of all planktic foraminifera per gram dry sediment; and H. Relative abundance of angular asymmetrical benthic foraminifera (AABF), an indicator of bottom water oxygenation. The grey bar marks the mid-Holocene transition in various proxy indicators
Figure 7.3.3 A comparison of core SK237 GC04 data (A) with representative marine and terrestrial records from the Arabian Sea and Asian subcontinent, namely SKI 7 5180ruber (Anand et al., 2008) (B); 63KA-41KL 818Oruber (Staubwasser et al., 2003) (C); ; Dongge Cave spelothem 5180 (Dykoski et al., 2005) (D); Guliya ice core 5180 (Thompson et al., 2012) (E) and RC27-23 815N (Altabet et al., 2002) (F). The vertical grey bar marks the mid-Holocene transition in various proxy indicators in both the SK237 GC04 core and terrestrial records
Figure 7.3.4 A comparison of SK237 GC04 core Mg/Ca SST (the black line is 3 point running average) (A), and 818Osw-iVc (B) with relative sea level (RSL) (1-ka moving Gaussian filter) (Grant et al., 2012) (C), atmospheric C0 2 (Monnin et al., 2001) (D), CH4 from European Project for Ice Coring in Antarctica (EPICA) (Loulerge et al., 2008) (E), change in total solar irradiance (ATSI) (Steinhilber et al., 2009) (F) and low- latitude insolation (Laskar et al., 2004) (G) during the Holocene. The vertical grey bar marks the mid-Holocene transition in various proxy indicators in both the SK237 GC04 core and other records
Figure 7.4.1 Location of core SK237 GC09 and western equatorial Pacific core ODP 806B (Lea et al., 2000) in the sea surface temperature map for the month o f April showing Indo Pacific Warm Pool (IPWP)
Figure 7.4.2 Changes in faunal and geochemical parameters in core SK237 GC09 during the last 45 ka. (A) SST, (B) 818CWe,-, (C)
184
185
187
195
196
XVII
Figure 7.4.3
Figure 7.4.4
518Osw, (D) TIC, (E) Corg, (F) coarse fraction (CF) (>63jim) and (G) abundance of planktic foraminifera per gram dry sediment
A comparison of SST (A) and 518Osw (B) of the southeastern 197 Arabian Sea with that in the western equatorial Pacific Ocean
during the last 45 ka
A comparison of (A) SK237 GC09 SST with (B) Greenland 198 ice core GISP2 S180 (Alley, 2004) and (C) Antarctica ice core
EPIC A Dome C 8D (Jouzel et al., 2007) during the last 45 ka
List o f T a b le s
Table No.
Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 5.1 Table 5.2
Table 5.3
Table 5.4 Table 6.1
Table 6.2 Table: 7.2.1
Table Title
Details of surface and subsurface samples used for the study Details of surface samples
Details o f AMS 14C dates of the core SK 237 GC 04 Details of AMS 14C dates of the core SK 237 GC 09
Number of superfamilies, families, genera and species belonging to six suborders reported from the present seas
Distribution of families, genera and species belonging to twenty-eight superfamilies reported from the southestem Arabian Sea.
Distribution o f genera and species belonging to fourty-nine families reported from the southestem Arabian Sea
Distribution of various species belonging to One hundred four genera reported from the seas
Results of CCA analysis of generic abundance of foraminifera and environmental variables by applying automatic forward selection procedure
Genus abbreviations used in CCA analysis The details o f the cores plotted in Figure 7.2.1
Page No.
30 31 37 39 44 45
46 47 128
128 168
XIX
A c k n o w le d g e m e n t
Foremost, I would like to express my sincere gratitude to my guide Dr. Rajiv Nigam. His knowledge and experience not only helped me in my subject matter but also in many personal matters. His helping nature to a student was a blessing for me. Spending time with him was always a source of learning.
Dr. Rajeev Saraswat, Senior Scientist, National Institute of Oceanography (NIO), Goa, who has always been a source of inspiration to me, is my co-guide. It is him who introduced me to the field of micropaleontology. He took care of all my research related problems since day one till my thesis is finalized with a thorough review of my thesis.
His helping hand was always there in my personal matters too. I owe him a lot. Here I express my heartfelt gratitude towards him.
I take this opportunity to thank the Directors [Prof. Sunil Kumar Singh (present director) and Dr S.W.A. Naqvi (former)] of National Institute of Oceanography for allowing and providing laboratory facilities for my research work. I am thankful to the Dr. Kamesh Raju KA (present head of geological oceanography division) and Dr. B. Nagender Nath (former head), for allowing and approving the facilities to carry out field studies and to participate in many conferences and workshops.
I would like to thank Prof. Kotha Mahender, Head of the Department and Vice Chancellor’s nominee in my Faculty Research Committee, Department of Earth Science, Goa University for his constructive comments during my Ph.D. assessments. I thank Prof.
A.G. Chachadi, Member of my Faculty Research Committee and Prof. Arun V. Salker, Member of my Faculty Research Committee, Dean, Faculty of Natural Science, Goa University, Prof. G. N. Nayak, Marine Science Department, Goa University, for their valuable suggestions and comments during my Ph.D. and also their help in university administrative work.
I am very thankful to the Council of Scientific and Industrial Research (CSIR) for the financial support provided (CSIR- Senior Research Fellow) during Ph.D and also for funding the GEOSINKS project. I acknowledge the financial support by the Department of Science and Technology, Delhi in the form of Fast Track project to my Co-Supervisor.
I am thankful to Dr. V. Ramaswamy, Chief Scientist, NIO, Goa, for elemental analysis of sediment samples. My special thanks to Dr. C. Prakash Babu, Principal Technical Officer, NIO, Goa, for his help and cooperation in operating CO2 Coulometer and C, N analyser for elemental analysis. I thank Prof. David W. Lea, Department of Earth Science, University of California, Santa Barbara, USA for the elemental analysis and Prof. Andreas Mackensen, Alfred Wegner Institute for Polar and Marine Research, Bremerhaven, Germany for isotopic analysis.
In any field of research, finding the required references is one of the important and difficult task, and it becomes a headache if not freely available. In this regard I like to thank Dr. Satya Ranjan Sahu, Scientist, Library, NIO, Goa for his valuable suggestions and Mr. M. Mithun, Senior Technical Officer, NIO, Goa, for his guidance and help in finding the required material from the library and also from the web.
During my stay at NIO I was fortunate to have the blessing hand of Dr. Sujata Kurtarkar Raikar. Her presence was a source of encouragement, positivity and strength to move ahead. Discussion with her was always helpful, whether in subject related matter or personal problems. She was always there to encourage me when I needed one. I was also blessed with the helping hand of Dr Linshy V.N. I thank her for her valuable suggestions and guidance, not only in my research work but also in my personal problems. I am thankful to Dr. Rajani Panchang Dhumal for her time to time help, support and valuable suggestions in subject matter. I cannot forget the help and support o f Mrs Swati Bhonsely during the initial days of my joining. Here I take this opportunity to thank all my seniors from Micropaleontology Laboratory, Dr. Khare, Dr. Henriques, Dr. Mayenkar, Dr.
Chaturvedi, Dr. Mazumder, Dr. Rana, Mr. Shanmukha for their valuable suggestions and support.
Working in micropaleontology, spending days and nights in the Laboratory was not an easy job. I was fortunate to have a wonderful company of Manasa M., Dharmendra Pratap Singh, Thejasino Soukhrie, Syed Mohammad Saalim, Rupal Dubey, Nimmy P.M., Amrata Kaithwar and also the newly joined Sudhira R. Bhadra, Shripad R. Bandodkar and Ramanand Yadav, as my labmates, who created a nice environment to work with.
My special thanks to Manasa, Dharmendra and Theja for all their help and support and also for making the days memorable during different scientific cruises. A very special thank to Saalim for being with me during tough times. I will always remain indebted to him for all his help and support in my personal problems.
I would like to thank all my friends, Priyabrata Das, Mithun M., Sheetal Godad, Abhijit Sukla, Dushmanta Maharana, Gobardhan Sahu, Rudra Behera, Rubina Pednekar, Mamta Kauthankar in NIO for their encouragement, love and support. My special thanks to Gobardhan Sahu for his help in statistical analysis and Abhijit Sukla for his ready to help attitude, who was always there to help me in any software related difficulties.
I take this opportunity to thank National Center for Antarctic and Ocean Research (NCAOR) and Ministry of Earth Sciences, Government of India, for giving me an opportunity to participate in the Integrated Ocean Drilling Program (IODP) Expedition 353 (Indian monsoon) in the Bay of Bengal.
XXI
Finally, I convey my most precious gratitude to my family, Bapa, Maa, Deepak Da, Sita Bahu, Debansh and m y beloved wife Reena, without their love and support this thesis would not have been possible.
(Dines H
CHAPTER ON E
Introduction
Climate is a dynamic process and has been the governing factor o f life throughout the geological time. In the past, the rise and demise of many civilizations is suggested to be largely controlled by climate change (DeMenocal, 2001; Schug et al., 2013). It has become the biggest challenge faced by our planet today. The rapid change in climatic conditions as observed since the industrialization, apparently due to increase in greenhouse gases, necessitates a proper understanding of climate change and its future projections. The possible consequences of changing environmental conditions include, increase in seawater temperature, changes in monsoon pattern, sea level rise, etc.
However, a question remains unanswered, whether these changes are a part of natural processes or a result o f anthropogenic activities. Therefore it is essential to understand how the various components of the climate system interact and what can be expected in the future.
The tropical regions being the locale o f key processes including El-Nino Southern oscillation, warm pool, Indian Ocean dipole, are an important part o f global climate system. A majority of the tropical regions, especially Asia, are affected by the monsoon, a process modulated by differential land-ocean heating and movement of inter-tropical convergence zone (ITCZ). Among Asian countries, India, which is mainly an agriculture based economy, is largely affected by its unique seasonal monsoon system. The agriculture in India is mainly dependent on monsoon precipitation (Gadgil and Gadgil, 2006) which shapes our country’s economy. Therefore, improved monsoon prediction would not only strengthen our economy but also make us cautious from the future monsoon disasters like drought and flood. The state of the oceans, especially the tropical regions, is a key component of monsoon. Both the Arabian Sea and the Bay of Bengal, modulate precipitation in India. Out of these two basins, the physical state of the eastern Arabian Sea is crucial for initiation of southwest monsoon in India (Joseph et al., 2006).
The monsoon winds induced upwelling makes the Arabian Sea, one of the most 1
biologically productive zones in the world oceans (Qasim, 1977). The high productivity coupled with restricted circulation results in the Arabian Sea being one of the three large oxygen deficient zones o f the world ocean (Allan et al., 2006) and one of the major oceanic denitrification sites (Naqvi, 1987). The eastern Arabian Sea is well known for seasonally reversing water circulation, monsoonal upwelling, Arabian Sea mini warm pool, and oxygen minimum zone. The southeastern Arabian Sea is the western extreme of the equatorial Indo-Pacific warm pool, a region with sea surface temperature being more than 28°C, throughout the year (Yan et a l, 1992). The Indo-Pacific warm pool is a key component of global climate and variations in its extent or intensity have far reaching consequences for global climate (Fasullo and Webster., 1999). The southeastern Arabian Sea has high productivity during the southwest monsoon, and both shallow water hypoxia, as well as deeper water oxygen minimum zone (OMZ), have been reported from this region. Hence this region provides a unique opportunity to study the different facets related to monsoonal strength, biological productivity variation, mechanism of Indo- Pacific warm pool and formation of OMZ.
Continuous long-term data of key parameters is required to understand the influence of eastern Arabian Sea on regional and global climate, especially monsoon. The instrumental data of key climate components is short and unable to meet the requirement of a reliable prediction. Climate prediction requires continuous, long term, high resolution, regional paleoclimatic data. For climatic data before the instrumental era, we are completely dependent on the proxy as the data for this interval cannot be collected or measured directly going back in time or generated by experiments. In this regard, microfossils serve as a potential proxy not only in paleoclimatology but also in stratigraphy and paleoceanography (Sinha, 2007). Among different proxies, oceanic proxies are considered to be vital for paleoclimatic studies as they can provide continuous data of longer time scale and are preserved in a relatively undisturbed environment. Since oceans cover the major area of our planet, the amount of material received by the oceans from different sources including continent, cosmic bodies, volcanic activities and the organisms in the ocean, is immense. The deposits o f geological past are well preserved in the oceans, providing excellent archives for paleoclimatic studies. Out of different oceanic proxies, different characteristics of microorganism, foraminifera are one of the
most frequently used paleoclimatic and paleoceanographic proxy (Saraswat, 2015).
Because of the unique features like wide geographic and geologic distribution, sensitivity to different physical parameters, the capability of preserving the signatures of the changing parameters in their relatively hard test, foraminifera are immensely used for paleoclimatic reconstruction (Saraswat and Nigam, 2013). The foraminiferal studies can not only provide qualitative estimates of past climate but also quantitative changes in several key climate parameters, including temperature and salinity. The work done on foraminifera in the eastern Arabian Sea was reviewed (chapter two) to identify the gaps in our understanding o f past climate from this region.
In view of the foregoing, in the present study, an attempt is made to analyze marine sediment samples for their foraminiferal contents from the gaps identified, and results are presented in subsequent chapters.
3
CHAPTER TWO
Previous Studies
2.1 Introduction
The major foraminiferal and other paleoclimatic studies carried out from the southeastern Arabian Sea and adjacent regions have been reviewed. Many authors worked on applications of foraminifera in this region, and their work was well accepted nationally and internationally. The work included both paleoclimatic and paleoceanographic studies.
Extensive foraminiferal studies have been done from the Arabian Sea since Chapman (1895) and Hofker (1927; 1930) started working in the Indian Ocean. Earlier, Sastry (1963) documented a bibliography of papers on foraminiferal studies since 1939 from the Indian region. Later on, Bandy et al. (1971) synthesized the history o f research on Indian Ocean foraminifera. Setty (1982) presented a review of the foraminiferal studies from the west coast of India. Nigam and Khare (1995a) published a bibliography and highlighted the foraminiferal studies carried out along the west coast of India. In the last decade, Bhalla et al. (2007) presented a bibliography o f foraminiferal studies in the near-shore region of the western coast of India and Laccadives Islands. Theme-wise categorization of all published literature on foraminifera (fossil) is discussed below.
2.1.1 Studies on distribution of foraminifera
The documentation of surface distribution of foraminifera is essential to understand the effect of various ambient physico-chemical and biological parameters on foraminifera.
Such studies are the basis to develop/refine foraminiferal proxies for paleoclimatic reconstruction. The distribution of foraminifera in the southeastern Arabian Sea and nearby regions, has been studied by many authors. Being easily approachable, foraminiferal distribution was documented from many beaches o f the west coast of India.
Chaudhury and Biswas (1954) and Bhatia (1956) reported 12 and 46 species, respectively, from Juhu beach sands, Mumbai. From Gujarat coast, the reports include 37 species from Mandvi (Jain and Bhatia, 1978); 26 species from Veraval (Srivastava et al., 1984); 18 species from Okha (Bhalla and Lai, 1985); 95 species from Saurashtra
(Pandya, 1985); 26 species from Dwarka (Talib and Farooqui, 1994). From Goa region, the reports include 24 species from Baga (Rocha and Ubaldo, 1964), 36 species from Calangute (Bhalla and Nigam, 1979); 29 species from Colva (Bhalla and Gaur, 1987) and 44 species from Miramar-Caranzalem (Setty et al. 1984). The beaches from the southern west coast are least studied where 25 species were reported from Malabar coast (Bhalla and Raghav, 1980). Kathal et al. (2000) published a review on foraminifera from beaches of west and east coast of India and put them in the different faunal realm. Biswas Kurian (1953) recorded 22 species of foraminifera from Travancore coastal water. Sethulekshmi Amina (1958) described and sketched 114 species from Travancore coastal water.
Antony (1968) identified 164 species from the shelf area of the Kerala coast (Vizhingom to Cannanore). Setty and Guptha (1972) identified 15 planktic species from the shelf and slope regions of Karwar and Mangalore. Setty (1972) reported 22 planktic foraminifera from the shelf sediment off Kerala coast. Rao (1972) identified 22 planktic species from off Bombay region. Guptha (1973) reported 20 benthic species from the lagoon sediment of Karavatti Atoll (Laccadives). Seibold and Seibold (1973) discovered a new species Cassidella pannikari from the Kerala shelf. Setty (1974) reported 32 species of recent benthic foraminifera from the shelf sediment o f Kerala coast. Seibold (1975) reported 69 species of benthic foraminifera including one new species from the lagoon and coast of Cochin. Bhatia and Kumar (1976) reported 35 benthic species including Caribeanella species from Anjediv Island, Binge Bay. Nigam et a l (1979) listed 64 benthic foraminifera from Dabhol-Vengurla region, Arabian Sea. Setty and Nigam (1980b) presented microenvironments and foraminiferal distribution o f 72 dead and 32 living species within the neritic regime of the Dabhol-Vengurla sector. Rao et al. (1985) reported 52 species of foraminifera from the inshore water off Trivandrum. Zhang (1985) analyzed the living planktic foraminifera from the eastern Arabian Sea and reported more abundance but less species diversity at 0-10 m and abundant presence o f Globigeriniodes ruber and Globigerinoides sacculifer. Rao et al. (1987) reported 107 species from the islands of Lakshadweep Archipelago. Nigam (1987) reported 102 taxa of benthic foraminifera from the neritic environment (15-60 m) of Vengurla-Bhatkal area. Guptha et al. (1990) studied pre-monsoon living planktic foraminifera from the southeastern Arabian Sea. Naidu (1990) reported 22 planktic foraminifera from the western
5
continental margin (Off Marmagoa to off Karwar) of India. Rao et al. (1991) described the ecology and distribution of recent planktic foraminifera in the eastern Arabian Sea.
Rao et al. (1992) reported 25 planktic species from the northern end of Lakshadweep group of islands in the southeastern Arabian Sea. Naidu (1993) documented planktic foraminifera from the western continental margin of India. Rao and Balasubramanian (1996) identified 78 foraminiferal species from Cochin estuary. Rao and Jayalakshmy (1997) reported 28 species o f planktic foraminifera along the Kerala coast. Guptha et a l (1994) studied living planktic foraminifera from the southeastern Arabian Sea using plankton tows and found that Globigerinoides ruber and Globigerinoides sacculifer are the most abundant species while Globigerina bulloides is rare during the late summer monsoon. Nigam and Khare (1999) listed 177 species from the region off the central west coast of India. Nigam et al. (2000) identified 204 species and generated proxy data for paleodepth using two different morpho-groups. From the eastern Arabian Sea, Off Goa region, Mazumder et al. (2003) listed 195 species of benthic foraminifera. Saraswati (2007) reported 11 genera o f symbiont-bearing benthic foraminifera from the lagoon waters of Lakshadweep. Shukla (2008) published a monograph on larger benthic foraminifera from Indian sedimentary basins. Nisha and Singh (2012) studied benthic foraminifera from 19 surface samples off north Kerala. They recorded 59 species and demonstrated a relationship between the distribution of major benthic fauna and the sediment-size and organic carbon content across the inner shelf to upper slope. Recently, Gadi et al. (2015) studied the distribution of foraminifera from the intertidal region of Lakshadweep Archipelago. Even though the foraminiferal distribution has been extensively studied from a major portion of the western margin o f India, limited studies have been carried from the southeastern Arabian Sea.
2.1.2 Cluster analysis and ecological studies on benthic foraminifera
The statistical analysis helps in grouping benthic foraminifera in meaningful assemblages, that can then be used to reconstruct paleoclimate. Nigam and Sarupria (1981) performed cluster analysis to understand the ecology of living benthic foraminifera from inner shelf off Ratnagiri. Setty and Nigam (1982) described foraminiferal assemblages and organic carbon relationship in the benthic marine
ecosystem from five near shore to shallow neritic regions of the west coast of India.
Nigam and Thiede (1983) did a Q-mode factor analysis of recent foraminifera from the inner shelf of the central west coast of India. Henrique (1993) used cluster analysis from off the central west coast of India (Vengurla-Mangalore) and found shallow, deep and intermediate assemblages o f benthic foraminifera. Mayenkar (1994) performed both Q- mode and R-mode cluster analysis on foraminifera retrieved from sediments collected from off Mangalore-Kochi sector and showed depth dependence assemblages of benthic foraminifera in this region. Nisha and Singh (2012) performed cluster analysis on foraminifera from shelf and slope region off north Kerala from a water depth of 30 to 200 m and found four major biofacies. Again, a majority of these studies were carried out from the northern and central western margin o f India and covered only the shelf region.
2.1.3 New and first time reported species
Many new species have been discovered and several others have been reported for the first time from Indian water. Kurian (1951) reported the presence of Operculina granulose in the coastal water of Travancore. Seibold and Seibold (1973) discovered Cassidella pannicari a new species from Kerala shelf. Setty et al. (1983) reported Spiroloculina sp. an abnormal two apertured form for the first time from off Bombay- Daman region. Srinivasan and Rai (1992) identified a new, distinctive benthic foraminiferal genus, Neopleurostomella from the eastern Arabian Sea and the type species of this genus is Neopleurostomella indica. Khare (1994) reported Pavonina flabellifinormis for the first time in the Arabian Sea. Nigam et al. (2004) reported a rare agglutinated species Ammolagena clavata for the first time in the Arabian Sea, Indian Ocean region. Bharti and Singh (2013) reported a new species of benthic foraminifera Bulimina arabiansis from the Arabian Sea. The studies suggest the possibility of several endemic species from unexplored regions like the southeastern Arabian Sea. Such species, if reported, can be used to better reconstruct regional paleoclimatic changes.
2.1.4 Studies on morphological aspects of foraminifera
The morphology of foraminifera responds to ambient conditions and thus can be used to reconstruct paleoclimate. Setty and Nigam (1980a) observed excentricity and twinning in
7
Virgulinella pertusa. Nigam and Rao (1987) showed the implications of recent benthic foraminiferal proloculus size variation in paleoclimatic studies. Nigam (1988b) showed changes in benthic foraminiferal morphology as a result of the reproductive behavior of foraminifera, as a new tool for reconstruction o f paleoclimate. Nigam and Rao (1989) reported that the coiling direction is related to the reproductive mode in benthic foraminifera (Cavarotalia annectens). Nigam and Khare (1992b) described the relationship between coiling direction and dimorphic reproduction in benthic foraminifera. Nigam and Khare (1994b) showed the effect o f river discharge on the morphology of benthic foraminifera by studying the morpho-groups. Khare et al. (1995) described the distributional pattern of benthic foraminiferal morpho-groups from shelf region off Mangalore. Nigam and Khare (1995b) developed the relationship between river discharge and proloculus size of Rotalidium annectens. Naidu et al. (1989) showed bathymetry as one of the factors which controls the external test morphology of benthic foraminifera. The information on the effect of various parameters on the morphology of benthic foraminifera is thus limited from the eastern Arabian Sea.
2.1.5 Isotopic and elemental studies
The isotopic and elemental analysis of foraminifera from the eastern Arabian Sea has been carried out by several workers to understand its relationship with various ambient conditions. Duplessy and Blanc (1981) analyzed oxygen and carbon isotopic composition of three surface dwelling planktic foraminifera from the northern Indian Ocean, including several stations from the southeastern Arabian Sea. Nigam and Sarkar (1993) described the interrelationship between mean proloculus size, 5180 , S13C in benthic foraminifera and their relation with temperature and salinity from inner shelf o f west coast of India.
Ahmed and Labeyrie (1994) determined 8180 and 813C variation from glacial to Holocene from the eastern Arabian Sea. Tiwari et al. (2006) reported high-resolution stable oxygen isotope variations for the last ~2.8 kyr from the monsoon-runoff-dominated eastern Arabian Sea. Saraswat (2010) discussed the dissolution of initial chambers of planktic foraminifera and its implication of secretion at higher pH. Deshpande et al. (2013) described the spatio-temporal distribution of S180 , 8D and salinity from the surface water samples of Arabian Sea. Naik and Naidu (2014) described the consequences of using
Boron/Calcium ratio in Globigerinoides ruber as a proxy for pH and pC02 in the Arabian Sea. Naik (2016) compared the Mg/Ca ratio of two genotype sensu stricto and sensu lato of Globigerinoides ruber (white) from the eastern Arabian Sea and found that the relative proportion of each genotype varies through the different period. The studies suggest that even though the major factors affecting the stable isotopic and elemental ratio of foraminifera in the eastern Arabian Sea are same as that reported from other world oceans, there are regional differences in the extent of the effect o f individual seawater parameters.
2.1.6 Studies on sediment accumulation rate
Sediment accumulation rate is an essential input to collect appropriate cores. Somayajulu et al. (1999) determined the sedimentation rate on the continental margins of the eastern Arabian Sea by using 210Pb, 137Cs and I4C. They reported that the sedimentation rate in this region varies from 0.06 to 0.66 cm/year for short term (<100 years) whereas for long term (>1000 years) it varies from 0.004 to 0.13 cm/year. It was further suggested that accelerator mass spectrometer (AMS) radiocarbon dating o f well-cleaned planktic foraminifera is most suited for long-term chronology (<50000 years),. Pandarinath et al.
(2004) studied the sedimentation rates and its implications from the western continental margin of India. Singh et al. (in press) in a comprehensive review, reported spatio- temporal changes in sedimentation rate from the eastern Arabian Sea for the last 24 ka.
The review indicates that the southeastern Arabian Sea is one of the high sedimentation rate zones.
2.1.7 Studies on paleomonsoon reconstruction
Both the geochemical and faunal proxies have been used to reconstruct paleomonsoon from the eastern Arabian Sea. Duplessy (1982) reconstructed past monsoon changes by using the difference between S180 of planktic foraminifera during the last glacial maximum and Holocene from the northern Indian Ocean. Fontugne and Duplessy (1986) used carbon isotopic ratio and organic carbon content in the sediments and inferred that northeast monsoon circulation was the dominant feature in the northern Indian Ocean during last glacial period. Nigam (1988a) used the abundance o f Cavarotalia annectance
9
from the shelf region off Karwar in front o f Kalindi river to reconstruct past monsoon.
Nigam and Nair (1989) and Nigam et al. (1995) reported a cyclicity of 77 years in monsoon and its possible modulation by the Gleissberg solar cycle by using foraminifera.
Sarkar et al. (1990) reported a negative excursion up to l%o in the 6180 value of the planktonic foraminiferal species at the time o f last glacial maxima from the eastern Arabian Sea and attributed it to the increased transport of low salinity water from the Bay of Bengal to the Arabian Sea. Nigam et al. (1992) suggested morpho-groups of benthic foraminifera as an additional tool for paleomonsoon studies. Nigam and Khare (1992a) inferred high monsoon rainfall in 2000 BC and 1500 BC by using benthic foraminiferal morpho-groups and planktic foraminifera and also provided archeological evidence in support of these events. Nigam (1993) showed the importance of foraminifera in paleomonsoon studies. Nigam and Khare (1994a) reported a change in monsoon precipitation at around 2000 years BP from off Karwar region. Nigam and Khare (1999) reconstructed paleomonsoon precipitation based on benthic foraminiferal morpho-groups.
Sarkar et al. (2000a) reconstructed high-resolution monsoon record o f Holocene from the eastern Arabian Sea by using stable isotopic analysis. Sarkar et al. (2000b) reconstructed paleomonsoon and paleoproductivity of the northern Indian ocean from a sediment core collected from the eastern Arabian Sea and found a weaker summer monsoon at 18 kyr BP and stronger at 9 kyr BP, whereas up welling was reduced during LGM and vigorous at 9 kyr BP. Tiwari et al. (2005a) documented past southwest monsoon precipitation by using 5180 of planktic foraminifera from the southeastern Arabian Sea. In the eastern Arabian Sea (off Goa region), Singh (2007) presented preservation of aragonitic pteropods for the last 30 kyr where he suggested high biological productivity during intensified summer monsoon in late Holocene and further that the strong OMZ might have resulted during interstadial periods which leads to shallowing of the ACD. He also suggested a weak summer monsoon and low productivity during cold stadial periods leading to a weak OMZ and deepening of the ACD. Tiwari and Ramesh (2007) showed a good correlation between total solar irradiance (TSI) and 5lsO of three planktic foraminiferal species suggesting the solar connection in controlling Indian monsoon. Rao et al. (2008) described the implications of diagenetic and environmental processes during the late Quaternary from the eastern Arabian Sea by using S180 and magnetic records.
Khare et al. (2008) reconstructed monsoon variability of the last 2500 years over India from the region off Karwar and found a considerable decrease in the intensity of monsoon approximately around 2000 years BP which is followed by an increase in the intensity around 1000 years BP. Rao et al. (2010) investigated the geochemical, sedimentological and geomagnetic characteristics of the sediments and did isotopic analysis on different cores collected from the southeastern Arabian Sea and put a comparative study to better understand the climate, oceanography and digenetic conditions during the last 35 kyr. Banakar et al. (2010) suggested that eastern Arabian Sea climatology is influenced by global climate and local monsoon. Mohan and Gupta (2011) used planktic foraminifera from the southeast Arabian Sea to understand changes in the surface ocean driven by winter monsoon coinciding with the northern hemisphere glaciations (NHG) and found intense deep convective overturning caused by strong northeast monsoon winds related to the strengthening of NHG. Mahesh et al. (2011) reconstructed surface salinity changes during the last 32 kyr in the southeastern Arabian Sea. Kessarker et al. (2013) studied variation in Indian summer monsoon intensity during the last 16.7 kyr by using both elemental and isotopic studies. Shrivastav et al. (2016) discussed morphological variations of Globigerina bulloides and its importance in paleomonsoon studies. Even though a lot o f work has been done to understand past monsoon changes, a majority of it dealt with qualitative changes and had a coarse multi
centennial resolution.
2.1.8 Studies on sea surface salinity
The precipitation-evaporation budget controls the salinity, and thus the salinity is linked with the monsoon. Several efforts have been made to reconstruct past salinity to understand paleomonsoon changes. Banakar et al. (2005) reconstructed sea surface salinity during the LGM and Holocene and suggested that the eastern Arabian Sea was more saline (by ~1.5 psu) during LGM than Holocene. Chodankar et al. (2005) reconstructed surface salinity gradient from 8lsO for the last 100 kyr in the eastern Arabian Sea to understand past variation in Indian summer monsoon. All o f these studies were either only on the stable oxygen isotopic ratio or a combination of oxygen isotopic ratio and seawater temperature reconstructed from alkenone or Mg/Ca. The method has
11
