Foraminiferal Transfer Functions Research Articles

A multiproxy assessment of the western equatorial Pacific hydrography during the last 30 kyr

Sea surface temperature (SST) and salinity of the Western Pacific Warm Pool (WPWP) reflect global climate effects such as the El Niño–Southern Oscillation phenomenon. However, reconstructions of past changes in the WPWP from the geologic record vary depending on the specific proxy record used. Here we develop a multiproxy record of the last deglaciation from a radiocarbon‐dated sediment core (MD97‐2138) retrieved in the heart of the WPWP. SST reconstructions for the past 30,000 years based on planktonic foraminiferal Mg/Ca (Globigerinoides ruber and Globigerinoides sacculifer), alkenone unsaturation index, and foraminiferal transfer functions differ notably. Mg/Ca‐based SST estimates from the surface dwelling species G. ruber in MD97‐2138 indicate a larger surface cooling (3° ± 0.6°C) during the Last Glacial Maximum (LGM) than inferred from Mg/Ca ratios in G. sacculifer (2.3° ± 0.7°C), statistical transfer functions based on planktonic foraminiferal species assemblages, and Uk37′ (1°–2°C). These estimates are consistent with estimates from other WPWP cores, thereby suggesting that the discrepancy is due to proxy compatibility rather than differences in cores qualitity. Postdepositional dissolution above the lysocline might have altered the Mg/Ca‐based temperature estimates in our site, but this effect is insufficient to resolve discrepancies between Mg/Ca in G. ruber and the other proxies. We suggest that the lower estimates obtained from Mg/Ca in G. sacculifer, faunal transfer functions, and Uk37′ might reflect subsurface temperature changes rather than strict surface estimates. Accounting for potential artefacts, including dissolution and bioturbation, we suggest that the glacial WPWP SST was about 2.5° ± 0.7°C cooler than during the Holocene, whereas the subsurface/upper thermocline temperature change was only about 1.8° ± 0.7°C. Interpreting variations in δ18OSW in terms of salinity changes suggests a possibly slight decrease in surface salinity at the site of MD97‐2138 during the LGM. Though LGM freshening in MD97‐2138 is not robust to postdeposition dissolution effects, this inferred freshening appears to be a general feature of the western equatorial Pacific.

Developing detailed records of relative sea-level change using a foraminiferal transfer function: an example from North Norfolk, UK

This paper provides a brief overview of the transfer function approach to sea-level reconstruction. Using the example of two overlapping sediment cores from the North Norfolk coast, UK, the advantages and limitations of the transfer function methodology are examined. While the selected cores are taken from different sites, and display contrasting patterns of sedimentation, the foraminiferal transfer function distils comparable records of relative sea-level change from both sequences. These reconstructions are consistent with existing sea-level index points from the region but produce a more detailed record of relative sea-level change. Transfer functions can extract sea-level information from a wider range of sedimentary sub-environments. This increases the amount of data that can be collected from coastal deposits and improves record resolution. The replicability of the transfer function methodology, coupled with the sequential nature of the data it produces, assists in the compilation and analysis of sea-level records from different sites. This technique has the potential to bridge the gap between short-term (instrumental) and long-term (geological or geophysical) records of sea-level change.

Assessing sea-level data from Connecticut, USA, using a foraminiferal transfer function for tide level

Concerns surrounding possible future climate change, sea level rise, and their potential impacts on coastal environments, have stimulated research seeking to elucidate the relationship between ocean levels and climate at the (sub)century-scale. The need for increasingly precise reconstructions of relative sea-level change has, in-turn, driven the development of new methodologies capable of resolving fine-scale variability within salt-marsh sedimentary sequences. The use of salt-marsh foraminifera as precise indicators of past tide levels has played a central role in this process and is exemplified by a number of detailed studies conducted in Connecticut, USA. In this paper, we apply the most recent methodological advance in the reconstruction of relative sea-levels using salt-marsh foraminifera. We develop a foraminiferal transfer function for tide level, derived from the modern foraminiferal distributions of four Connecticut salt-marshes. In contrast to existing approaches that employ site-specific interpolations of local vertical foraminiferal assemblage zones, this transfer function can provide objective, quantitative and reproducible estimates of palaeomarsh-surface elevation with explicitly stated error terms for marshes throughout Connecticut, irrespective of differences in tidal range. We demonstrate the foraminiferal transfer function approach by employing it to reconstruct changes in palaeomarsh-surface elevation from three cores recovered from Hammock River marsh, Connecticut. The resulting reconstructions, which are precise to ±0.09 m, are tested using an independent dataset from the neighbouring state of Maine, and are used to assess a pivotal record of mean high water (MHW) change from this site. We conclude that the transfer function reconstructions show good general agreement with previous records of palaeomarsh-surface elevation, but with the advantages of quantified error terms and a transparent, reproducible methodology. This replicability will assist in the comparison or combination of local records of MHW change to infer large-scale, regional sea-level variations.

Patterns of export production in the eastern equatorial Pacific over the past 130,000 years

Productivity at six core locations in the eastern equatorial Pacific (EEP) was reconstructed with a benthic foraminiferal transfer function. The core records show strong regionality, especially where affected by Peru margin upwelling of deeper Equatorial Undercurrent Water (EUC) (originally coming from the subantarctic). This “Peru margin” record differs from that seen along the equator where divergence leads to shallow upwelling, and it is generally inverse to that seen in cores outside the areas of equatorial upwelling. Principal components analysis shows that the main productivity pattern correlates well to the global oxygen isotope record and has lowest values during isotope stages 2 and 4. In addition to this, equatorial cores show a higher frequency pattern of variation which becomes much more pronounced during MIS 3 and 2. The reconstructions based on benthic foraminifera were tested against those from nonaccumulation rate based inorganic chemical proxies of export production. These were found to correlate well in the region influenced by Peru upwelling, and also to share common features for sites along the equator. All the nonaccumulation rate based paleotracers are consistent with one another and differ from accumulation rate derived proxies. The differences between the two classes of paleotracers may result from uncertainties in calculating actual biogenic fluxes since 230Th‐normalized results conform more to those we obtained. Analysis of planktonic carbon isotope values for the EEP, and their comparison to the record of the Pacific subantarctic, indicates that the subantarctic contribution to the EUC was reduced during MIS 3 and 2.

Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence

Multi-proxy data and radiocarbon dates from several key cores from the Black Sea and Marmara Sea document a complex paleoceanographic history for the last ∼30 000 yr. The Marmara Sea was isolated from both the Black Sea and the Aegean Sea during glacial periods when global sea-level lowering subaerially exposed the shallow sills at the Straits of Bosphorus and Dardanelles (i.e. lake stage), and reconnected through both straits during interglacial periods, when rise of global sea level breached the shallow sills (i.e. gateway stage). Micropaleontological data show that during the ‘lake stage’ the surface-water masses in both the Marmara Sea and Black Sea became notably brackish; however, during the ‘gateway stages’ there was a low-salinity surface layer and normal marine water mass beneath. Two sapropel layers are identified in the Marmara Sea cores: sapropels M2 and M1 were deposited between ∼29.5 and 23.5 ka, and ∼10.5 and 6.0 ka, respectively. Micropaleontological and stable isotopic data show that the surface-water salinities were reduced considerably during the deposition of both sapropel layers M2 and M1, and calculation using planktonic foraminiferal transfer functions shows that sea-surface temperatures were notably lower during these intervals. The presence of fauna and flora with Black Sea affinities and the absence of Mediterranean fauna and flora in sapropels M1 and M2 strongly suggest that communication existed with the Black Sea during these times. A benthic foraminiferal oxygen index shows that the onset of suboxic conditions in the Marmara Sea rapidly followed the establishment of fully marine conditions at ∼11–10.5 ka, and are attributed to Black Sea outflow into the Marmara Sea since 10.5 ka. These suboxic conditions have persisted to the present. The data discussed in this paper are completely at odds with the ‘Flood Hypothesis’ of Ryan et al. (1997), and Ryan and Pitman (1999).

A High-Resolution Sea-Surface Temperature Record from the Tropical South China Sea (16,500–3000 yr B.P.)

The timing and magnitude of sea-surface temperature (SST) changes in the tropical southern South China Sea (SCS) during the last 16,500 years have been reconstructed on a high-resolution, 14C-dated sediment core using three different foraminiferal transfer functions (SIMMAX28, RAM, FP-12E) and geochemical (Uk′37) SST estimates. In agreement with CLIMAP reconstructions, both the FP-12E and the Uk′37 SST estimates show an average late glacial–interglacial SST difference of 2.0°C, whereas the RAM and SIMMAX28 foraminiferal transfer functions show only a minor (0.6°C) or no consistent late glacial–interglacial SST change, respectively. Both the Uk′37 and the FP-12E SST estimates, as well as the planktonic foraminiferal δ18O values, indicate an abrupt warming (ca. 1°C in <200 yr) at the end of the last glaciation, synchronous (within dating uncertainties) with the Bølling transition as recorded in the Greenland Ice Sheet Project 2 (GISP2) ice core, whereas the RAM-derived deglacial SST increase appears to lag during this event by ca. 500 yr. The similarity in abruptness and timing of the warming associated with the Bølling transition in Greenland and the southern SCS suggest a true synchrony of the Northern Hemisphere warming at the end of the last glaciation. In contrast to the foraminiferal transfer function estimates that do not indicate any consistent cooling associated with the Younger Dryas (YD) climate event in the tropical SCS, the Uk′37 SST estimates show a cooling of ca. 0.2–0.6°C compared to the Bølling–Allerød period. These Uk′37 SST estimates from the southern SCS argue in favor of a Northern Hemisphere-wide, synchronous cooling during the YD period.

Mid‐ to late Holocene relative sea‐level change in Poole Harbour, southern England

AbstractA foraminiferal transfer function for mean tide level (MTL) is used in combination with AMS radiocarbon dated material to construct a record of relative sea‐level (RSL) change from Poole Harbour, southern Britain. These new data, based on multiple cores from duplicate sites, indicate four phases of change during the last 5000 cal. (calendar) yr: (i) rising RSL between ca. 4700 cal. yr BP and ca. 2400 cal. yr BP; (ii) stable to falling RSL from ca. 2400 cal. yr BP until ca. 1200 cal. yr BP; (iii) a brief rise in RSL from ca. 1200 cal. yr BP to ca. 900 cal. yr BP, followed by a period of stability; (iv) a recent increase in the rate of RSL rise from ca. 400–200 cal. yr BP until the present day. In addition, they suggest that the region has experienced long‐term crustal subsidence at a rate of 0.5 mm C14 yr−1. Although this can account for the overall rise in MTL observed during the past 2500 yr, it fails to explain the changes in the rate of rise during this period. This implies that the phases of RSL change recorded in the marshes of Poole Harbour reflect tidal range variations or ‘eustatic’ fluctuations in sea‐level. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Reconstructing relative sea-level change using UK salt-marsh foraminifera

The position of past sea levels can be reconstructed using a series of sea-level index points that possess information on age, location, altitude, and a quantified vertical relationship with a former tidal frame (the “indicative meaning”). Whilst these points fix the altitude of relative sea-level at one instant in time, they provide no information on its variation between them. Here, a foraminiferal transfer function is used to reconstruct changes in water depth from fossil assemblages preserved within salt-marsh sediments. The transfer function performs reliably in the high marsh zone, where agglutinated foraminiferal species are dominant. In lower marsh environments where calcareous species are prevalent, postmortem test dissolution alters the fossil assemblages and leaves them without modern analogues. To circumvent this problem, a new transfer function based on agglutinated foraminifera and utilising preserved test linings is developed. This new transfer function significantly reduces the number of samples without modern analogues, but at the expense of diminished sensitivity in the low marsh environment. Additionally, the transfer function is used to establish a series of sea-level index points that place observed lateral shifts in depositional environment into a vertical and temporal context. The combination of age-altitude and high-resolution water-level reconstructions offers the potential to obtain more detailed and reliable records of relative sea-level change from salt-marsh sediments.

Paleo‐sea surface temperature calculations in the equatorial east Atlantic from Mg/Ca ratios in planktic foraminifera: A comparison to sea surface temperature estimates from U37K′, oxygen isotopes, and foraminiferal transfer function

We present two ∼270 kyr paleo‐sea surface temperature (SST) records from the Equatorial Divergence and the South Equatorial Current derived from Mg/Ca ratios in the planktic foraminifer Globigerinoides sacculifer. The present study suggests that the magnesium signature of G. sacculifer provides a seasonal SST estimate from the upper ∼50 m of the water column generated during upwelling in austral low‐latitude fall/winter. Common to both down‐core records is a glacial‐interglacial amplitude of ∼3°–3.5°C for the last climatic changes and lower Holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5.5 and glacial stage 6 temperatures, respectively. The comparison to published SST estimates from alkenones, oxygen isotopes, and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods.

Planktonic Foraminiferal and Alkenone Records of the Last Deglaciation from the Eastern Arabian Sea

The oxygen isotope record of planktonic foraminifera from tropical core MD77194 (Eastern Arabian Sea) exhibits a clear two-step deglaciation with a brief δ18O transient event. In the tropics, this δ18O maximum could correspond to a cooling or to a change in the δ18O content of sea water. In this study, past sea-surface temperature (SST) and primary production (PP) are reconstructed from foraminiferal transfer functions and compared to values estimated from alkenone measurements. SST and PP records from both proxies indicate a 1.5–2.5°C deglacial warming, coupled with a PP decrease, and a 0.5–1°C cooling during the Younger Dryas (YD). A detailed comparison between independent micropaleontological and geochemical proxies helps us identify potential biases and thus strengthen the paleo-reconstructions.

Foraminiferal faunal estimates of paleotemperature: Circumventing the No‐analog problem yields cool Ice Age tropics

The sensitivity of the tropics to climate change, particularly the amplitude of glacial‐to‐interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no‐analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods. A new calibration strategy developed here, which uses past variability of species to define robust faunal assemblages, solves the no‐analog problem and reveals ice age cooling of 5° to 6°C in the equatorial current systems of the Atlantic and eastern Pacific Oceans. Classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core‐top assemblages misrepresented the ice age faunal assemblages. Our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by Climate: Long‐Range Investigation, Mapping, and Prediction (CLIMAP) [1981] and thus may help to resolve a long‐standing controversy. Our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems, however, and supports CLIMAP's inference of stability of the subtropical gyre centers.

Assessment of sea surface temperature variations in the central North Atlantic using the alkenone unsaturation index (U 37k′)

A high resolution record of U 37 k′ -derived SST estimations has been obtained in a core from the central North Atlantic Ocean (SU90/08, 43°30′N, 30°24′W) spanning a time period of 280 ky. The general trend of the U 37 k′ profile parallels closely the δ 180 signal and represent an independent confirmation that the SST variations in the glacial-interglacial time scales are correlated with the northern ice sheets evolution. In contrast to the CLIMAP (1984) conclusions based on the foraminiferal transfer function technique, the SST during the last interglacial period (LIP, isotopic stage 5.5) are 2–3°C warmer than during the Holocene. This result is in good agreement with many studies based in coastal and continental records that strongly suggest warmer climatic conditions over North America and Europe. Finally, the SST estimates during the last glacial maximum (LGM, 18 ky bp) where 4.5°C cooler than during the previous glacial period (PGP, stage 6). We argue that this difference is caused by a northward position of the polar front during the PGP in the Central North Atlantic.

Testing the effects of tropical temperature, productivity, and mixed‐layer depth on foraminiferal transfer functions

Statistical transfer functions relate living planktonic foraminiferal species of the central equatorial Pacific to measured sea surface temperature, integrated primary productivity, and mixed‐layer depth. The faunal estimates successfully reconstruct latitudinal patterns observed in both warm (El Niño, February–March 1992) and cool (La Niña, August–September 1992) seasonal settings. Predictions of mixed‐layer depth appear to be unbiased by temperature or productivity in our data set but tend to underestimate deep mixed layers. Interactions between productivity and temperature, perhaps through their common influence on respiration and growth rates, bias foraminiferal transfer functions for both properties. Paleoceanographic estimates may be improved by accounting for such biological processes that translate the environment into a faunal response preserved in the geologic record.

The impact of seasonality on the benthos as reflected in the assemblages of deep-sea foraminifera

A surface sediment study of benthic foraminiferal assemblages in the eastern Pacific (Loubere, 1994) yielded a regression equation for estimating surface ocean productivity from assemblage composition with an r 2=0.98. This equation was tested with samples from locations outside the calibration data set area and yielded estimates with an error of about 11% of the estimate. The estimation equation has an r 2=0.86 for the non-calibration data set samples. This equation was then applied to surface sediment samples from the Indian Ocean, which represent benthic conditions identical to those of the Pacific calibration data set, except that surface ocean productivity in the Indian Ocean is highly seasonal. There is relatively little seasonal variation in productivity over the areas sampled for the Pacific calibration data. Although it is difficult to quantify average annual surface ocean productivity in the Indian Ocean, it appears that the benthic foraminiferal transfer function yields estimates of only qualitative value. At highest productivities it is likely that the equation underestimates productivity. Using Discriminant Function Analysis to compare sample groups from the Pacific and Indian Oceans representing identical environmental conditions, except for seasonality, shows that the Indian Ocean samples are increasingly anomalous, or “no-analog”, from the Pacific Ocean perspective as productivity increases. At higher productivities, Indian Ocean samples are deficient in Uvigerina species, Chilostomella sp., Pullenia sp. and E. tumidulus while having an excess of E. exigua, C. hooperi, Gyroidina grp. species, B. mexicana and Nonion species, from the Pacific viewpoint. The differences in benthic foraminiferal assemblages between the two oceans can be ascribed to changes in benthic community structure that occur as organic carbon flux to the seabed becomes increasingly episodic or seasonal. Overall, Indian Ocean foraminiferal assemblages follow compositional trends similar to those seen in the Pacific Ocean as surface productivity changes. Hence, a Pacific based benthic foraminiferal transfer function can still reasonably estimate productivity gradients from Indian Ocean assemblages. However, there are 4 sufficient assemblage differences between the two oceans to make seasonality a variable that should be incorporated in a calibration data set, and to make estimation of paleo-seasonality a possibility.

Holocene and Pleistocene glacial palaeoceanography off southeastern Australia, based on foraminifers and nannofossils in Vema cored hole V18–222∗

Sea‐surface temperature trends in planktonic foraminifers, isotopic and population abundance trends in benthic foraminifers, and abundance trends in calcareous nannofossils of V18–222 (38°34'S, 140°37'E, southeast Australia: 1904 m water depth) reveal an interglacial interval (oxygen isotope stage 1) distinctly different from underlying glacial intervals (isotope stages 10 and 12). During the glacial times mean sea‐surface temperatures (FI‐2 planktonic foraminiferal transfer function) ranged between 12°C and 9°C, indicating the close proximity of the Subtropical Convergence Zone. The cooler waters were unfavourable for the existence of the nannofossil Florisphaera profunda, while cooler water flora like Coccolithus pelagicus and Gephyrocapsa caribbeanica flourished. Absence of tropical and subtropical nannoflora suggest that the Leeuwin Current did not flow across the area at this time. High surface productivity, associated with strong upwelling during this time is indicated by Bulimina aculeata‐dominated benthic foraminiferal populations, and by Uvigerina spp. depleted in δ13C. At depth it is likely that the core site was immersed in Circumpolar Deep Water. In contrast, during interglacial stage 1 and the end of stage 2 deglaciation, mean sea‐surface temperatures at the site ranged between 14°C and 18°C, similar to modern temperatures. High summer sea‐surface palaeotemperatures indicate that the Subtropical Convergence was positioned well south of the site during the last ∼14 000 years. The persistent presence of a warm‐water nannoflora indicates that the Leeuwin Current flowed over the area throughout warm extremes in climate through the last ∼14 000 years. Anomalously low winter sea‐surface palaeotemperatures during the same time, however, coupled with the persistent presence of Florisphaera profunda in low abundance, indicate a persistence of mild upwelling activity in the area, similar to that which exists today, since ca 14 ka. Stable deep‐water conditions during the interglacial are indicated by benthic foraminiferal population trends with a fauna dominated by Bulimina striata and uniform, but relatively high, δ13C signals in Uvigerina spp., with the site immersed in a mixture of Antarctic Intermediate Water and Antarctic Circumpolar Water.

Hydrographic changes of the Southern Ocean (southeast Indian Sector) Over the last 230 kyr

Hydrographical changes of the southern Indian Ocean over the last 230 kyr, is reconstructed using a 17‐m‐long sediment core (MD 88 770; 46°01′S 96°28′E, 3290m). The oxygen and carbon isotopic composition of planktonic (N. pachyderma sinistra and G. bulloides) and benthic (Cibicidoides wuellerstorfi, Epistominella exigua, and Melonis barleeanum) foraminifera have been analysed. Changes in sea surface temperatures (SST) are calculated using diatom and foraminiferal transfer functions. A new core top calibration for the Southern Ocean allows an extension of the method developed in the North Atlantic to estimate paleosalinities (Duplessy et al., 1991). The age scale is built using accelerator mass spectrometry (AMS) 14C dating of N. pachyderma s. for the last 35 kyr, and an astronomical age scale beyond. Changes in surface temperature and salinity clearly lead (by 3 to 7 kyr) deep water variations. Thus changes in deep water circulation are not the cause of the early response of the surface Southern Ocean to climatic changes. We suggest that the early warming and cooling of the Southern Ocean result from at least two processes acting in different orbital bands and latitudes: (1) seasonality modulated by obliquity affects the high‐latitude ocean surface albedo (sea ice coverage) and heat transfer to and from the atmosphere; (2) low‐latitude insolation modulated by precession influences directly the atmosphere dynamic and related precipitation/ evaporation changes, which may significantly change heat transfer to the high southern latitudes, through their control on latitudinal distribution of the major frontal zones and on the conditions of intermediate and deep water formation.

Surface and deep hydrology of the Northern Atlantic Ocean during the past 150000 years

The abrupt shifts in foraminiferal δ18O observed in core ODP 609 (the meltwater signature of the Heinrich events, see Bondet al.1992 b,1993) are seen in ten North Atlantic high sedimentation rate cores; the decreasing south-west to north-east gradient is well pronounced. This confirms that the Heinrich events are associated with major surges of the Laurentide ice sheet, when it is believed approximately 106km3 of ice are liberated during each event. A tentative reconstruction of the changes in surface and deep-water density, based upon the study of cores SU 90-39 (53° N 22° W) and SU 90-08 (43° N 30° W), is presented. To calculate the density of surface water, sea surface temperature is obtained using a foraminiferal transfer function (see CLIMAP 1981) and salinity is estimated using the foraminiferal δ18O record corrected for the temperature effect on isotopic fractionation. The density of deep water is directly derived from the benthic δ18O record, after corrections for the mean global changes in Ocean δ18O. Results indicate that the North Atlantic Ocean has been repetitively a potential area of deep-water formation during the last glacial period.

Glacial‐Holocene carbonate dissolution and sea surface temperatures in the south China and Sulu seas

Sediment cores from the South China and Sulu seas have been used to study sea surface temperature changes in these two western equatorial Pacific basins during the last 25,000 years. Sea surface temperature (SST) estimates were derived using the planktonic foraminiferal transfer function FP‐12E previously developed by Thompson (1981). The water depths for the cores range from 500 m to more than 4,000 m and thus provide a good opportunity to evaluate the effect of carbonate dissolution on quantitative paleotemperature estimates. The sea surface temperature time series from shallow, well‐preserved cores indicate that average winter and summer temperatures during the Holocene were approximately 27°C and 29.5°C, respectively, for both the South China and Sulu seas. These estimates agree well with modern observations. During the last glacial maximum, summer sea surface temperatures were approximately 28.5°C in the South China Sea and 29°C in the Sulu Sea and thus were very similar to the Holocene. In contrast, glacial winter sea surface temperatures are estimated at approximately 21°C for the South China Sea and 24°C for the Sulu Sea. This decrease in glacial winter sea surface temperatures results in a much larger seasonality during the last glacial (5°‐8°C) compared to the Holocene (2°C). These seasonal contrasts are much greater than those estimated by Climate: Long‐Range Investigation, Mapping, and Prediction Members (1981) for this region of the western equatorial Pacific. Variation in intensity of the monsoon system and surface water exchange rates between these basins and the open ocean are the major factors controlling glacial‐interglacial SST fluctuations in the South China and Sulu seas. One factor influencing the accuracy of the SST estimates is the quality of preservation of the planktonic foraminiferal assemblages. Our results demonstrate that depth‐dependent increases in dissolution result in systematically cooler SST estimates. This is due to the fact that warm water planktonic foraminifera tend to be more solution susceptible, and as dissolution progresses, the assemblage becomes enriched in the more resistant, cooler water taxa. Since dissolution is more intense during interglacials than glacials in the Pacific, dissolution tends to reduce the amplitude of the glacial‐interglacial temperature difference.