Globigerinoides Ruber Research Articles

Analysis of Abundance and Origin Possibility of Planktonic Foraminifera in Sulawesi Sea

Foraminifera is very diverse and adaptive, both in its morphology and biology. It is a potential bioindicator to understand the ecological and physical conditions of the ancient and modern waters based on their distribution. It has been well confirmed that the abundance of foraminifera (as a fossil) in sediment can reflect the ocean conditions above (mixed layer to upper ocean) where it was deposited. Planktonic foraminifera however can be considered as passive particles, their movement is carried by ocean currents. In consequence, the foraminifera abundance may represent more wider ocean condition according to the ocean current pattern. This study aims to examine the role of ocean currents in the distribution of foraminifera in the Sulawesi Sea. Ten gravity core sediment samples from 73-3009 m water depth were retrieved by RV Geomarin III from the Marine Geological Institute, Indonesia. We conducted quantitative analysis, including calculation of abundance and cluster analysis. Two decades (1992-2012) of ocean current simulated data from the Hybrid Coordinate Ocean Model (HYCOM) is used in this analysis, extending from 115°E-140°E and 8°N-2°S. The result indicates that planktonic foraminifera is abundant in the Sulawesi Sea by 86.3%. There were several predominant planktonic species such as Globigerinoides ruber (22.6%), Globigerina bulloides (15.3%), and Neoglobuquadrina dutertrei (10.1%). The ocean current above the sample location is constantly moving eastward as a part of the NECC. The average currents velocity shows that foraminifera in sample site S-03 with depth 2064 m may originated from up to 1035 kilometers away from its recent location.

Population dynamics and reproduction strategies of planktonic foraminifera in the open ocean

Abstract. It has long been assumed that the population dynamics of planktonic foraminifera is characterised by synchronous reproduction associated with ontogenetic vertical migration. However, due to contradictory observations, this concept became controversial, and subsequent studies provided evidence both in favour and against these phenomena. Here we present new observations from replicated vertically resolved profiles of abundance and shell size variation in four species of planktonic foraminifera from the tropical Atlantic to test for the presence, pattern, and extent of synchronised reproduction and ontogenetic vertical migration in this oceanic region. Specimens of Globigerinita glutinata, Globigerinoides ruber ruber, Globorotalia menardii and Orbulina universa were collected over the first 700 m resolved at nine depth intervals at nine stations over a period of 14 d. Dead specimens were systematically observed irrespective of the depth interval, sampling day and size. Conversely, specimens in the smaller size fractions dominated the sampled populations at all times and were recorded at all depths, indicating that reproduction might have occurred continuously and throughout the occupied part of the water column. However, a closer look at the vertical and temporal size distribution of specimens within each species revealed an overrepresentation of large specimens in depths at the beginning of the sampling (shortly after the full moon) and an overrepresentation of small individuals at the surface and subsurface by the end of the sampling (around new moon). These observations imply that a disproportionately large portion of the population followed for each species a canonical reproductive trajectory, which involved synchronised reproduction and ontogenetic vertical migration with the descent of progressively maturing individuals. This concept is consistent with the initial observations from the Red Sea, on which the reproductive dynamics of planktonic foraminifera has been modelled. Our data extend this model to non-spinose and microperforate symbiont-bearing species, but contrary to the extension of the initial observations on other species of foraminifera, we cannot provide evidence for ontogenetic vertical migration with ascent during maturation. We also show that more than half of the population does not follow the canonical trajectory, which helps to reconcile the existing contrasting observations. Our results imply that the flux of empty shells of planktonic foraminifera in the open ocean should be pulsed, with disproportionately large amounts of disproportionately large specimens being delivered in pulses caused by synchronised reproduction. The presence of a large population reproducing outside of the canonical trajectory implies that individual foraminifera in a fossil sample will record in the calcite of their shells a range of habitat trajectories, with the canonical trajectory emerging statistically from a substantial background range.

The response of calcareous plankton to the Sapropel S1 interval in North Ionian Sea

A high resolution study of calcareous nannofossils has been performed on samples from the Sapropel S1interval deposited in the North Ionian Sea, with the aim to assess the paleoenvironmental changes in the photic zone during this crucial interval in Mediterranean circulation. Calcareous nannofossil data have been integrated with planktonic foraminiferal data recently published from which the paleoclimatic curve has been constructed. Placoliths (namely Emiliania huxleyi) and Florisphaera profunda distributions, along with that of planktonic foraminifer Globigerinoides ruber white, evidence that, after a progressive weakening of surface water mixing, a deep chlorophyll maximum developed just prior to the sapropel deposition. We suggest that these changes took place as a response to enhanced precipitation conditions and riverine discharge as testified by increasing trend of reworked coccoliths and the occurrence of lower salinity taxon Braarudosphaera bigelowii. Calcareous nannofossils also point out that the oceanographic (water column stratification, reduced bottom water ventilation) and biogeochemical (increased primary production) processes that occurred during the S1 formation were particularly dominant during the earliest part of the older S1 warm phase (S1a). Our results support than some re-ventilation events of the shallow depth of studied site (665 m) occurred to some extent, particularly during the final phases of S1a. The distribution of holococcoliths, more abundant during the cold interruption phase S1i, seems confirm that the preservation of these tiny and delicate coccoliths, highly susceptible to dissolution, is enhanced under seafloor re-ventilation conditions. Finally, we tentatively suggest that preservation also plays a significant role in the distribution of the warm upper photic zone taxa, particularly during the warm S1b interval.

Symbiont Photosynthesis and Its Effect on Boron Proxies in Planktic Foraminifera

AbstractBoron proxies in the calcium carbonate shells of planktic foraminifera are sensitive to seawater acidity, but B/Ca ratios and isotopic composition (i.e., δ11B) recorded by different foraminifer species grown under identical environmental conditions differ significantly and systematically. Specifically, Globigerinoides ruber displays higher B/Ca and δ11B than Trilobatus sacculifer and Orbulina universa. It has been hypothesized that these differences are caused by species‐specific rates of symbiont photosynthesis and habitat depth with greater symbiont photosynthesis elevating the microenvironmental pH of G. ruber relative to T. sacculifer and O. universa. Here we test this hypothesis by applying fast repetition rate fluorometry (FRRF), Chlorophyll a quantification, and symbiont counts in laboratory grown specimens of G. ruber (pink), T. sacculifer and O. universa to study species‐specific differences in symbiont photochemical quantum efficiencies. In addition, we report B/Ca shell profiles measured by laser ablation on the same specimens previously monitored by FRRF, and δ11B data of discrete populations of all three species grown under high and low light conditions in the laboratory. While the light experiments document that symbiont photosynthesis elevates pH and/or δ11B in the calcifying microenvironment of all three foraminifer species, the FRRF, Chl. a and symbiont abundance data are relatively uniform among the three species and do not scale consistently with intrashell B/Ca, or with observed species‐specific offsets in B/Ca or δ11B. Implications of these findings for foraminiferal physiology and biomineralization processes are discussed.

Roles of insolation forcing and CO2 forcing on Late Pleistocene seasonal sea surface temperatures

Late Pleistocene changes in insolation, greenhouse gas concentrations, and ice sheets have different spatially and seasonally modulated climatic fingerprints. By exploring the seasonality of paleoclimate proxy data, we gain deeper insight into the drivers of climate changes. Here, we investigate changes in alkenone-based annual mean and Globigerinoides ruber Mg/Ca-based summer sea surface temperatures in the East China Sea and their linkages to climate forcing over the past 400,000 years. During interglacial-glacial cycles, there are phase differences between annual mean and seasonal (summer and winter) temperatures, which relate to seasonal insolation changes. These phase differences are most evident during interglacials. During glacial terminations, temperature changes were strongly affected by CO2. Early temperature minima, ~20,000 years before glacial terminations, except the last glacial period, coincide with the largest temperature differences between summer and winter, and with the timing of the lowest atmospheric CO2 concentration. These findings imply the need to consider proxy seasonality and seasonal climate variability to estimate climate sensitivity.

Surface hydrographic changes at the western flank of the Sicily Channel associated with the last sapropel

In the eastern Mediterranean Sea, the early Holocene was characterized by major climatic and oceanographic changes that led to the formation of the last sapropel (S1) between 10.8 and 6.1 kyr cal. BP. These hydrographic changes might have altered the water exchange between the eastern and western Mediterranean sub-basins through the Strait of Sicily, but the existing evidences are inconclusive. In the present study we show new evidence from sediment core NDT-6-2016 located at the western flank of the Sicily channel, a key location to monitor the surface/intermediate water exchange between the two Mediterranean sub-basins. We perform paleo-hydrographic reconstructions based on planktic foraminifera ecology for the last 15 kyr cal. BP, including the S1 deposition interval. In addition, δ 18 O measurements in both Globigerina bulloides and Globigerinoides ruber and also major elements analyses in bulk sediment are presented. Our results show that significant changes in surface water properties occurred in W-Sicily characterized by a strong contrast in the seasonal hydrographic conditions during the S1 interval. This study proposes that the oceanographic changes in the eastern Mediterranean associated with the surface freshening promoted by the African monsoon likely triggered a restricted water exchange through the Strait of Sicily. This situation led to limited influence of the surface Atlantic waters into the studied area that favored the development of intense summer stratification and vertical winter mixing. This situation changed at about 7 kyr cal. BP when a decrease in the summer stratification probably reflected the influence of the eastward path of the surface Atlantic Waters. This situation would suggest a reinforcement of the water exchange through the Strait of Sicily that marked the end of the extreme conditions that prevailed in the eastern Mediterranean during the S1 formation. • Surface hydrographic reorganization related to the sapropel S1 is observed for the first time in the central Mediterranean. • The acquired data provide new evidences of a restricted sea surface water exchange during the S1 across the Strait of Sicily. • Paleo-hydrographic reconstructions are based on planktic foraminifera ecology, major element analyses and δ 18 O measurements.

Indian monsoon wind variability since ~11 kyr in the northwestern and northeastern Arabian Sea

• We studied varying monsoon wind stress in the Arabian Sea during the Holocene . • Surface productivity was high during the early Holocene . • Summer monsoon was weak and winter monsoon was strong in the middle Holocene. • Monsoon winds show high spatial variability in strength in the Arabian Sea. In this paper, we use planktic foraminifera and mixed-layer species from cores SK-240/327, SK-243/I- and ABP-25/03, northeastern Arabian Sea to investigate monsoon wind variability. Planktic foraminifera include Globigerina bulloides, a monsoon proxy and mixed-layer species Globigerinoides ruber, Gs. sacculifer, Gs. obliquus and Gs. extremus from cores SK-240/327, SK-243/I-1 and ABP-25/03 encompassing last ~11 calibrated kilo years before the Present (~11 cal kyr BP). The population abundances of Globigerina bulloides and mixed-layer species were compared with published Globigerina bulloides percentages from the western Arabian Sea Ocean Drilling Program Holes 723A, 724B and 727B, and eastern Arabian Sea core ABP-25, 02 to understand variations in Indian monsoon winds during the Holocene. In the eastern Arabian Sea, upwelling induced productivity was higher during 10–6.5 cal kyr BP which decreased during 6.5–3 cal kyr BP. In the northwestern Arabian Sea, we observe a similar scenario but not every site captured this change owing to spatial diverseness in monsoon wind stress. The productivity increased since 3 cal kyr BP due to intense summer monsoon winds in the northeastern Arabian Sea, whereas productivity began to increase at ~1.5 cal kyr BP in the northwestern Arabian Sea. The upwelling intensity shows large spatial and temporal variations in the eastern and western Arabian Sea, indicating varying monsoon wind strength across the Arabian Sea during the Holocene. The spectral analysis performed on Globigerina bulloides shows cyclicity which is associated with solar variability during the past 11 kyr record in the northeastern Arabian Sea.

Variability in Indonesian Throughflow Upper Hydrology in Response to Precession‐Induced Tropical Climate Processes Over the Past 120 kyr

AbstractThe Indonesian Throughflow (ITF), as the sole low‐latitude conduit connecting the Pacific and Indian Oceans, regulates the thermohaline balance between these oceans. Thus, investigating the variability in the ITF and its relationship with the precessional forcing is crucial for understanding the drivers of tropical climate change. Here, we reconstruct the history of the ITF over the past ∼120 kyr based on high‐resolution (∼400 years) δ18O and Mg/Ca records of Globigerinoides ruber and Pulleniatina obliquiloculata from core SO217‐18540 retrieved from the Flores Sea upwelling region within the main pathway of the ITF. A comparison of these new records with published paleo‐oceanographic and climatological data from the western tropical Pacific Ocean suggests that annual mean conditions in the Flores Sea were controlled by ITF variability rather than by monsoonal upwelling. Our results further indicate that precessional insolation was a major forcing for the hydrological evolution of the ITF during the past 120 kyr. We suggest that the precessional insolation forcing paced ITF variability by modulating the mean state of El Niño‐Southern Oscillation‐like conditions and latitudinal shifts and/or expansion/contraction of the Intertropical Convergence Zone.

Holocene Evolution of Sea‐Surface Temperature and Salinity in the Gulf of Mexico

AbstractFlows into and out of the Gulf of Mexico (GoM) are integral to North Atlantic Ocean circulation and help facilitate poleward heat transport in the Western Hemisphere. The GoM also serves as a key source of moisture for most of North America. Modern patterns of sea‐surface temperature (SST) and salinity in the GoM are influenced by the Loop Current, its eddy‐shedding dynamics, and the ensuing interplay with coastal processes. Here, we present sub‐centennial‐scale records of SST and stable oxygen isotope composition of seawater (18Osw; a proxy for salinity) over the past 11,700 years using planktic foraminiferal geochemistry in sediments from the Garrison Basin, northwestern GoM. We measured O and magnesium‐to‐calcium ratios in tests of Globigerinoides ruber (white) to generate quantitative estimates of past sea‐surface conditions. Our results replicate and extend late Holocene reconstructions from the Garrison Basin, using which we then create composites of SST and 18Osw. We find considerable centennial and millennial‐scale variability in both SST and 18Osw, although their evolution over the Holocene is distinct. Whereas mean‐annual SSTs display pronounced millennial‐scale variability, 18Osw exhibits a secular trend spanning multiple millennia and points to increasing northwestern GoM surface salinity since the early Holocene. We then synthesize the available Holocene records from across the GoM and alongside the Garrison Basin composite uncover substantial, yet regionally consistent, spatiotemporal variability. Finally, we discuss the role of the Loop Current and coastal influx of freshwater in imposing these heterogeneities. We conclude that dynamic surface‐ocean changes occurred across the GoM over the Holocene.

Meridional migration of Indian Ocean Monsoon precipitation during the early Holocene: Evidence from the Andaman Sea

The Holocene evolution of the Indian Ocean Monsoon (IOM), especially the spatiotemporal nature of its maximum precipitation period, remains controversial. Here we reconstruct high-resolution local δ18Osw and sea surface temperature (SST) values by pairing Mg/Ca values and the δ18O data from planktonic foraminifera Globigerinoides ruber (white) in the southern Andaman Sea in order to understand IOM rainfall variability during the Holocene. Local δ18Osw values show that local maximum rainfall occurred between 10.6 ka and 8.6 ka in the southern Andaman Sea, before declining markedly during the 8.6–5.0 ka period, and then decreasing slightly after 5.0 ka. The Mg/Ca-SST was relatively low during the 10.3–8.6 ka period, before increasing slightly between 8.6 ka and 4.0 ka; it declined thereafter. But the sedimentation rate at the site of Core ADM-C1 relating to monsoonal precipitation of the source region of sediments exhibited its highest value during the 8.6–5.5 ka period. After making further comparisons with other published records for this region, we would propose that maximum IOM precipitation during the early Holocene has exhibited a clearly meridional migration: it was located in the tropics around 7°N during the 10.6–8.6 ka period, migrated northward to the subtropics during the 8.6–5.5 ka period, before migrating southward again after 5.0 ka. We would suggest that the northward shift of maximum precipitation during the Early Holocene in the IOM region was in response to the progressively northward migration of the Intertropical Convergence Zone (ITCZ) and the change of El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) activities.

Paleoclimatic responses in the tropical Indian Ocean to regional monsoon and global climate change over the last 42 kyr

Paleoclimatic teleconnections between monsoon-dominated regions and the northern Atlantic has been revealed in the tropical Indian Ocean. Millennial-scale climate variability, as registered in Greenland ice cores, was transferred to the low-latitude regions by changes in the Atlantic meridional overturning circulation (AMOC). However, there is still some disputes regarding the mechanism of climatic variation in the tropical Indian Ocean. To explore the interplay responses to regional monsoons and global in the northeastern Indian Ocean, here we present new evidence of trace elements (Mg/Ca and Ba/Ca) and stable isotopes measured from the planktonic foraminifera Globigerinoides ruber (white) in core ADM-159, which was collected from the central Andaman Sea. Twelve accelerator mass spectrometry (AMS) radiocarbon dates of the planktonic foraminifera Neogloboquedrina dutertrei from the core provide a reliable age model. Our results indicate gradual surface warming with several short-lived fluctuations since ~42 kyr ago. The SST during the Last Glacial Maximum (LGM) was ~3 °C colder than the present SST, and a sharp increase in warming beginning at 18.5 cal ka BP indicated the transition from the LGM to the Holocene; these matched well with the warming trend in the Antarctica and the Southern Ocean and the rise in atmospheric CO2 levels. The seawater δ18O record (defined as δ18Osw, presumably salinity-driven) and the Ba/Ca record, which is a measure of the continental riverine runoff from Myanmar, revealed a prominent millennial-scale variability pattern controlled by the Indian summer monsoon (ISM) as seen in speleothem records. The higher salinity values that suggested weakened ISM precipitation and a decrease in freshwater output from the Irrawaddy-Salween rivers were seen at 41.1 cal ka BP–39.9 cal ka BP, 34.9 cal ka BP–32.8 cal ka BP, 29.3 cal ka BP–28 cal ka BP, 25.7 cal ka BP–23.8 cal ka BP, 19.3 cal ka BP–15.8 cal ka BP, 13 cal ka BP–11.4 cal ka BP, and 4.0 cal ka BP–2.3 cal ka BP, reflecting strong correspondence with cold events in North Atlantic. Thus, this study provides evidence that climatic changes in the tropical Indian Ocean responded well to both regional monsoon and global climate changes, and during that atmospheric CO2, solar insolation, and AMOC played the most important roles in those responses.

Tropical Atlantic stratification response to late Quaternary precessional forcing

The upper ocean circulation in the western tropical Atlantic (WTA) is responsible for the northward cross-equatorial heat transport as part of the Atlantic Meridional Overturning Circulation (AMOC). This cross-equatorial transport is influenced by the thermocline circulation and stratification. Although seasonal thermocline stratification in the WTA is precession-driven, the existence of an orbital pacemaker of changes in the entire WTA upper ocean stratification, which comprises the main thermocline, remains elusive. Here, we present a 300 ka-long record of the WTA upper ocean stratification and main thermocline temperature based on oxygen isotopes (δ18O) and Mg/Ca of planktonic foraminifera. Our Δδ18O record between Globigerinoides ruber and Globorotalia truncatulinoides, representing upper ocean stratification, shows a robust precession pacing, where strong stratification was linked to high summer insolation in the Northern Hemisphere (precession minima). Mg/Ca-based temperatures support that stratification is dominated by changes in thermocline temperature. We present a new mechanism to explain changes in WTA stratification, where during the Northern Hemisphere summer insolation maxima, the Intertropical Convergence Zone shifts northward, developing a negative wind stress curl anomaly in the tropical Atlantic. This, in turn, pulls the main thermocline up and pushes the South Atlantic Subtropical Gyre southwards, increasing the stratification to the north of the gyre. This mechanism is supported by experiments performed with the Community Earth System Model (CESM1.2). Finally, we hypothesize that the precession-driven WTA stratification may affect the cross-equatorial flow into the North Atlantic.

Latitudinal Differentiation among Modern Planktonic Foraminiferal Populations of Central Mediterranean: Species–Specific Distribution Patterns and Size Variability

Studies of the spatial distribution and size of modern planktonic foraminifera are still lacking in the Mediterranean Sea. In this study, 17 core-top sediments collected from a north-south transect along the central Mediterranean have been analyzed for planktonic foraminiferal content, in terms of their distributional pattern and intraspecific size variability. Among the analyzed planktonic foraminiferal species, Globigerina bulloides and Globigerinoides ruber (w) were the most abundant, presenting an antagonistic behavior and an overall decreasing trend in their average size values from Adriatic to Ionian sub-basins. Intraspecific differences have been also documented for G. ruber (w), with the dominant sensu stricto morphotype to present generally higher frequencies and more constant shell sizes than sensu lato. The greater size variability of the latter is possibly related to its adaptation in particular hydrographic conditions based on its depth habitat preference and ecological characteristics to reach the (sub)optimum growth conditions. The rest of the species occur in minor percentages and show on average 11% increase with decreasing latitude characterized by distinct species-specific size variations along the transect. Our results show that the relationship between planktonic foraminifera shell size and abundance or sea surface temperature are either absent or weaker than previously reported for other regions and that in central Mediterranean assemblages’ size may be mainly related to nutrient availability. Besides the environmental parameters (sea surface temperature, primary productivity, water depth, stratification), the possible hidden cryptic diversity, still lingers to be consistently determined, could give a better understanding of the geographic and morphological differentiation within the Mediterranean planktonic populations.

Foraminiferal Abundance at the Western Water of Kai Islands, Molucca Province, Related to Oceanographic Condition

Foraminifera is a single-celled marine organism known as a potential proxy for (paleo)environment and (paleo)oceanography conditions. It also has been widely used as an indicator of coral reef health. We analyzed microfauna foraminifera from nine core top of marine sediments. Marine sediments have been collected by gravity core from western Water of Kai Islands, on board Geomarin III of MGI. The study aims to understand the microfaunal community and the oceanographical condition of Kai islands. The result indicates the high abundance and diversity of foraminifera, comprised of 95 species, including 28 species of planktonic and 67 benthic species. Planktonic type is very dominant (95.4% on average), typical for a bathyal environment. The dominant species are Neogloboquadrina dutertrei (21.21% on average), Globorotalia menardii (16.67% on average), Globigerina bulloides (11.73%), and Pulleniatina obliqueloculata (7.83%). Those are indicator species for a high productivity environment. However, Globigerinoides ruber, an oligotrophic warm water type, is also abundant (13.86% on average). Furthermore, the dominant genera of benthic types are Bolivina, Bulimina, dan Uvigerina (1.2% on average). This finding indicates relatively eutrophic and warm water conditions of west waters surrounding Kai Islands, with dysoxic bottom water conditions.

Paleoceanographic significance of Globigerinoides ruber (white) morphotypes from the Andaman Sea

Globigerinoides ruber (white), a tropical to sub-tropical planktonic foraminiferal species which dwells in the mixed layer, has garnered significant attention of paleoceanographic investigations. Recent studies on G. ruber (w) morphotypes (G. ruber sensu stricto (s.s.) and G. ruber sensu lato (s.l.)) have inferred differences in seasonal calcification depths and offsets in isotopic and elemental data. To decipher if the morphotype abundances vary in response to changes in Indian Summer Monsoon (ISM), two well-dated sediment cores from the Andaman Sea, a core monsoon area in the northeastern Indian Ocean, are investigated. The abundance variations of G. ruber s.s. are very similar to total G. ruber (w), whereas G. ruber s.l. is very sensitive to the hydrologic changes linked to the ISM variability. Increased abundances of G. ruber s.l. were observed during periods of weak stratification and the resultant increase in productivity. The last glacial maximum (LGM), deglacial, Younger Dryas (YD) and late Holocene periods with weak ISM are characterized by a high abundance of G. ruber s.l. Conversely, this morphotype abundance decreased from 30 to 23 ka, Bølling/Allerød (B/A), early and mid-Holocene when the ISM was enhanced. The large variation of G. ruber morphotypes in the Andaman Sea is attributed to the selective preference of nutrient-rich water which varied with water column changes (salinity-controlled stratification) associated with ISM evolution. The elevated abundances of G. ruber s.l. during the glacial period closely match with the available records from other regions, possibly making them potential climatic markers.

Strong solar influence on multi-decadal periodic productivity changes in the central-western Bay of Bengal

Oceanic productivity is a vital component of the global carbon cycle. The productivity in the tropical oceans is strongly modulated by the monsoon winds. The monsoon winds are driven by the temperature. Therefore, the oceanic productivity is most likely to be influenced by the increasing global warming. However, the projected response of oceanic productivity to global warming is ambiguous. The past records can help to better constrain the future response of oceanic productivity to different warming scenarios. Here, we reconstruct decadal monsoon and productivity changes from the central-western Bay of Bengal, covering the entire Holocene. We use both foraminiferal (relative abundance of Globigerina bulloides, stable oxygen isotopic ratio of surface dwelling Globigerinoides ruber) and geochemical [calcium carbonate (CaCO3), organic carbon (Corg), organic carbon/total nitrogen (Corg/TN)] proxies to reconstruct productivity and associated parameters. All the proxy data suggests a large variation in productivity and carbon burial during the Holocene. A very intense upwelling, concomitant with a phase of increased precipitation and CaCO3 burial is inferred during the beginning of Greenlandian (~12,000 - ~10,000 yrs BP). The intense upwelling, however, did not result in higher organic carbon burial. The beginning of Northgrippian (~8000–7000 yr BP) was a significantly wet phase followed by gradual decrease in precipitation. Incidentally, the reduced upwelling during the Northgrippian was synchronous with a large increase in organic carbon burial. The opposite trend in upwelling intensity and %Corg during the Meghalayan as well, suggests decoupling of upwelling induced productivity and organic carbon burial in the western Bay of Bengal. Towards the late Meghalayan (after ~1500 yr BP), we report a relatively enhanced precipitation with continual increase in CaCO3 but with reduced Corg burial. Further, these long-term variations were accompanied by significant short-term periodic changes, closely resembling Gleissberg cycle as well as Seuss cycle, suggesting a possible link with the solar variability.

Central Equatorial Pacific Cooling During the Last Glacial Maximum

AbstractEstablishing tropical sea surface temperature (SST) during the Last Glacial Maximum (LGM) is important for constraining equilibrium climate sensitivity to radiative forcing. Until now, there has been little data from the central equatorial Pacific in global compilations, with foraminiferal assemblage‐based estimates suggesting the region was within 1°C of modern temperatures during the LGM. This is in stark contrast to multi‐proxy evidence from the eastern and western Pacific and model simulations which support larger cooling. Here we present the first estimates of glacial SST in the central equatorial Pacific from Mg/Ca in Globigerinoides ruber. Our results show that the central Pacific cooled by about 2.0°C during the LGM, in contrast with previous global compilations but in agreement with models. Our data support a larger magnitude of tropical LGM cooling, and thus a larger equilibrium climate sensitivity, than previous studies which relied on foraminiferal assemblages in the central tropical Pacific.

Planktic foraminiferal δ18O values indicate precipitation variability in the southeastern South China Sea over the last 175 ka BP

The South China Sea (SCS) is an important research area of the tropical water cycle and an important pathway by which the Asian monsoon transports water vapor and heat from the tropical ocean to the Asian continent, yet its response to low-latitude tropical processes is poorly resolved. Here, we report high-resolution records of the oxygen isotopes (δ18O) of planktic Globigerinoides ruber and Globorotalia menardii at different depths and Mg/Ca ratios from a core in the southeastern SCS over the last 175 ka BP to discuss the variability of sea surface temperature (SST) and salinity (SSS) patterns, which can provide insights into understanding SCS hydroclimate dynamics. The records show that SST was characterized by glacial-interglacial cycles largely controlled by ice volume and orbital insolation-driven changes in monsoon circulation. Several short high-frequency intervals of high SST in the glacial periods and low SST in the stadial periods corresponded to variations involving enhanced winter or summer monsoons. The variation in δ18O is obviously influenced by monsoon-driven SSS. Although the δ18O values in different areas of the SCS were similar, the comparison shows that the δ18O values in the study area were lower than those in the northern SCS but higher than those in the southern SCS, appearing to reveal the tropical water cycle process of evaporation, transmission and rainfall in the SCS. The negative deviation in δ18O peaks indicated heavy precipitation in the southeastern SCS caused by an enhanced convection intensity and strengthened summer monsoons. A valuable set of surface and subsurface Δδ18OG.r-G.m (Δδ18OG. ruber - Δδ18OG. menardii) records proved that more negative δ18O shifts must be closely related to the surface seawater environment. However, negative shifts in δ18O were controlled by different mechanisms during the glacial and interglacial periods. In the interglacial periods, the northward shift of the intertropical convergence zone (ITCZ) and summer solar insolation played a key role in precipitation, whereas in the glacial periods, El Niño events and differences in the thermal properties between the sea and land dominated.

Assessing the effect of riverine discharge on planktic foraminifera: A case study from the marginal marine regions of the western Bay of Bengal

Planktic foraminifera are amongst the most widely used paleoclimatic proxies. The application of foraminifera for paleoclimatic reconstruction requires knowledge of the ecological preference of species. Here, we report the surface distribution and ecology of planktic foraminifera from 99 core top samples collected from the riverine influx dominated western Bay of Bengal. The riverine influx reduces the planktic population on the shelf, in its immediate vicinity. Incidentally, the population increases on the slope in front of the major river mouths. A total 30 species belonging to 14 genera were found. Globigerinita glutinata is the most abundant species in the western Bay of Bengal, followed by Globigerina bulloides. Globigerina bulloides is abundant on the outer shelf, a region influenced by upwelling during southwest monsoon. The negative correlation of Neogloboquadrina dutertrei with sea surface salinity is attributed to the chlorophyll maximum due to the density gradient created by the hyposaline surface water. Globigerinoides ruber were abundant (>10%) at stations with higher salinity (>32 psμ). The mixed layer dwelling Trilobatus sacculifer are abundant on the slope. The increased relative abundance of Globigerinella siphonifera in shallow waters is attributed to the low salinity freshwater plume. The negative correlation of Globorotalia menardii with thermocline temperature and positive correlation with thermocline salinity suggests its cold water, high salinity habitat. We conclude that the freshwater and sediment influx and associated changes strongly modulate planktic foraminiferal distribution. The findings will help in better application of temporal changes in planktic foraminiferal population to reconstruct past environmental conditions from the Bay of Bengal.

Climate variability since last glacial maximum based on distribution of foraminifera in North Papua Waters, Pacific Ocean

Foraminifera distribution is one of the proxies used to reconstruct climatic conditions and paleoceanography. Specific species or groups of foraminifera can be associated with certain oceanographic parameters. As one of the entrances of Indonesia Through Flow (ITF), North Papua Waters has the role of channeling water masses from the Pacific Ocean to the Indonesian Waters. It is also influenced by global thermohaline circulation and ENSO. In this study, observations were made of changes in the distribution of foraminifera to reconstruct paleoclimate and paleoceanographic conditions in the North Papua Waters and their relation to global climate conditions. The analysis was performed on 246 cm core sediments with eight cm foraminifera observation intervals at sample depths 246-126 cm and four cm at sample depths of 126-0 cm. Pulleniatina spp., Neogloboquadrina spp., and Globorotalia spp., are used for radiocarbon dating. Planktonic abundant species of foraminifera are Pulleniatina obliqueloculata, Neogloboquadrina dutertrei, Globorotalia menardii, Globigerinoides ruber, Globigerinoides trilobus, and the benthonic are Melonis pompilideus, Pullenia bulloides, Oolina sp., Planulina bradyii, Oridorsalis umbonatus, Cibicides subhaidingerii, Eggrela bradyii, Planulina wuelestroffi, and Quinqueloculina spp.,. Division according to cluster analysis can show the difference between Holocene and Pleistocene, which is then more detailed divided into 17 clusters. Based on biozonation there are some events that can be observed: climate variability since Late Pleistocene, record Pleistocene-Holocene boundary based on the significant variability of foraminifera distribution, and records some of the global climate events such as Last Glacial Maximum (~19-17 kyr), Younger Dryas (~11-9 kyr), and 8,2K event.