Planktic δ18O Research Articles

Global Evidence of Obliquity Damping in Climate Proxies and Sea-Level Record during the Last 1.2 Ma: A Missing Link for the Mid-Pleistocene Transition

A recent research has identified an inverse amplitude link between obliquity damping and short eccentricity amplification during the Mid-Late Pleistocene based on LR04 δ18O and equatorial Pacific Site 846 sea surface temperature records that is associated with the Earth’s long-term cooling. In the present study, new evidence of this anticorrelation is presented from Antarctic δD-CO2-CH4 records, global benthic–planktic δ18O, and regional (Atlantic, Pacific, Mediterranean, and Indian) climate-related proxies. Based on a critical review of theoretical constraints (Earth’s oblateness changes and ice-volume phase lag in the obliquity band <5.0 kyr), this widespread and symmetric (bipolar) obliquity response damping has been interpreted as an effect of the obliquity–oblateness feedback, which could be the latent physical mechanism at the origin of the Mid-Pleistocene Transition (MPT). Indeed, results and considerations of the present work suggest that fast and positive/negative net variation in the Earth’s oblateness in the obliquity band was controlled by a dominant glacio-eustatic water mass component and, assuming a rapid response of the ice volume to surface temperature changes, the mean obliquity lag response is estimated to be <5.0 kyr over the past 800 kyr. These elements may explain the interglacial/glacial damping observed in the obliquity response. The consolidation of the Earth’s long-term icy state in the subtrend IV, culminating with the post-MPT obliquity damping, might have contributed to the strengthening of the short eccentricity response by mitigating the obliquity ‘ice killing’ during obliquity maxima (interglacials), favouring the obliquity-cycle skipping and a feedback-amplified ice growth in the short eccentricity band (obliquity damping hypothesis). This suggests a different impact of the climate friction than what is generally believed, which is presumably the latent physical mechanism that triggers the transient ‘competitive’ interaction between obliquity and short eccentricity started early during the Piacenzian.

Revisiting Oxygen‐18 and Clumped Isotopes in Planktic and Benthic Foraminifera

AbstractForaminiferal isotopes are widely used to study past oceans, with different species recording conditions at different depths. Their δ18O values record both seawater oxygen‐18 and temperature according to species‐specific fractionation factors, while their Δ47 signatures likely depend only on temperature. We describe an open‐source framework to collect/combine data relevant to foraminiferal isotopes, by constraining species‐specific oxygen‐18 fractionation factors (18α) based on culture experiments, stratified plankton tows or core‐top sediments; compiling stratified plankton tow constraints on living depths for planktic species; extracting seawater temperature, δ18O, and chemistry from existing databases for any latitude, longitude, and depth‐range; inferring calcification temperatures based on the above data. We find that although 18α differs between species, its temperature sensitivity remains indistinguishable from inorganic calcite. Based on > 2,600 observations we show that, although most planktic δ18O values are consistent with seawater temperature and δ18O over their expected living depths, a sizable minority (12%–24%) have heavier‐than‐predicted δ18O, best explained by calcification in deeper waters. We use this framework to revisit three recent Δ47 calibration studies of planktic/benthic foraminifera, confirming that planktic Δ47 varies systematically with oxygen‐18‐derived temperature estimates, even for samples whose δ18O disagrees with assumed climatological conditions, and demonstrating excellent agreement between planktic foraminifera and modern, largely inorganic Δ47 calibrations. Benthic foraminifera remain ambiguous: modern benthic Δ47 values appear offset from planktic ones, yet applying equilibrium Δ47 calibration to the Cenozoic benthic foraminifer record of Meckler et al. (2022, https://doi.org/10.1126/science.abk0604) largely reconciles it with δ18O‐derived temperatures, with discrete Δ47/δ18O discrepancies persisting in the Late Paleocene/Eocene/Plio‐Pleistocene.

A 1.5-million-year record of orbital and millennial climate variability in the North Atlantic

Abstract. Climate during the last glacial period was marked by abrupt instability on millennial timescales that included large swings of temperature in and around Greenland (Daansgard–Oeschger events) and smaller, more gradual changes in Antarctica (AIM events). Less is known about the existence and nature of similar variability during older glacial periods, especially during the early Pleistocene when glacial cycles were dominantly occurring at 41 kyr intervals compared to the much longer and deeper glaciations of the more recent period. Here, we report a continuous millennially resolved record of stable isotopes of planktic and benthic foraminifera at IODP Site U1385 (the “Shackleton Site”) from the southwestern Iberian margin for the last 1.5 million years, which includes the Middle Pleistocene Transition (MPT). Our results demonstrate that millennial climate variability (MCV) was a persistent feature of glacial climate, both before and after the MPT. Prior to 1.2 Ma in the early Pleistocene, the amplitude of MCV was modulated by the 41 kyr obliquity cycle and increased when axial tilt dropped below 23.5∘ and benthic δ18O exceeded ∼3.8 ‰ (corrected to Uvigerina), indicating a threshold response to orbital forcing. Afterwards, MCV became focused mainly on the transitions into and out of glacial states (i.e. inceptions and terminations) and during times of intermediate ice volume. After 1.2 Ma, obliquity continued to play a role in modulating the amplitude of MCV, especially during times of glacial inceptions, which are always associated with declining obliquity. A non-linear role for obliquity is also indicated by the appearance of multiples (82, 123 kyr) and combination tones (28 kyr) of the 41 kyr cycle. Near the end of the MPT (∼0.65 Ma), obliquity modulation of MCV amplitude wanes as quasi-periodic 100 kyr and precession power increase, coinciding with the growth of oversized ice sheets on North America and the appearance of Heinrich layers in North Atlantic sediments. Whereas the planktic δ18O of Site U1385 shows a strong resemblance to Greenland temperature and atmospheric methane (i.e. Northern Hemisphere climate), millennial changes in benthic δ18O closely follow the temperature history of Antarctica for the past 800 kyr. The phasing of millennial planktic and benthic δ18O variation is similar to that observed for MIS 3 throughout much of the record, which has been suggested to mimic the signature of the bipolar seesaw – i.e. an interhemispheric asymmetry between the timing of cooling in Antarctica and warming in Greenland. The Iberian margin isotopic record suggests that bipolar asymmetry was a robust feature of interhemispheric glacial climate variations for at least the past 1.5 Ma despite changing glacial boundary conditions. A strong correlation exists between millennial increases in planktic δ18O (cooling) and decreases in benthic δ13C, indicating that millennial variations in North Atlantic surface temperature are mirrored by changes in deep-water circulation and remineralization of carbon in the abyssal ocean. We find strong evidence that climate variability on millennial and orbital scales is coupled across different timescales and interacts in both directions, which may be important for linking internal climate dynamics and external astronomical forcing.

The first appearance of Glacial North Atlantic Intermediate Water (GNAIW) during the Mid-Pleistocene transition

The Mid-Pleistocene Transition (MPT) is arguably the most prominent shift in the Earth's climate system during the entire Pleistocene. It is characterized by a shift from a ∼ 40 kyr to a ∼ 100 kyr glacial cyclicity, going in hand with considerable growth of glacial continental ice-sheets. In search for potential drivers of these changes in the cryosphere, a slow-down of deep ocean circulation has been proposed as an important factor that might have reduced the atmospheric pCO2 level and thus created boundary conditions favourable for pertaining large ice-sheets. Additionally, as argued for the Last Glacial Maximum, enhanced production of intermediate waters might enhance intermediate to deep oceanic stratification and thus suppress CO2 release from the deep ocean and thereby reduce atmospheric greenhouse gas concentrations. To investigate potential changes in the North Atlantic intermediate water-mass configuration across the MPT we utilize δ18O and δ13C records obtained on the deep thermocline-dwelling foraminifera Globorotalia crassaformis from mid-latitude International Ocean Discovery Program (IODP) Site U1313. In conjunction with benthic and planktic δ18O and δ13C data from reference sites for Labrador Sea Water (IODP Site U1305) and intermediate water formation in the north-eastern North Atlantic (Ocean Drilling Program Site 982) our data show that major changes in the production and dispersal of intermediate water masses took place across the MPT. In particular, we note a shoaling of glacial intermediate waters commencing with Marine Isotope Stage (MIS) 22, which we interpret as the first occurrence of Glacial North Atlantic Intermediate Water, a prominent constituent of Late Pleistocene glacial water masses in the Atlantic Ocean. We further infer that the amount and vertical position of the warm and saline Mediterranean Outflow Water (MOW) had a major impact on the spatial configuration of North Atlantic intermediate water masses during the MPT, due to its capacity to modulate subsurface heat transport and isopycnal configuration. Our new findings thus provide evidence for a so far underestimated role of intermediate water circulation in shaping oceanic and potentially atmospheric changes during the MPT.

An exceptional record of millennial-scale climate variability in the southern Iberian Margin during MIS 6: Impact on the formation of sapropel S6

The study of planktic and benthic δ18O at site U1389 in the Gulf of Cadiz allowed us to reconstruct climate variability during the penultimate glacial period at an unprecedented millennial scale resolution. Hereby, a sequence of interstadial-stadial episodes similar to the Dansgaard-Oeschger events recorded during Marine Isotope Stage (MIS)3, were recognized in MIS6. After a detailed correlation with millennial-scale variability recorded along the Iberian margin and the North Atlantic we were able to link the millennial changes next to the Iberian Peninsula with Antarctic climate variability due to the interhemispheric seesaw response of the Atlantic circulation. The straight coupling at site U1389 of a) the planktic δ18O that reflects climate change in the Atlantic with b) the benthic δ18O, which records the temperature and oxygen isotope composition of the mixture of Mediterranean Outflow and Atlantic intermediate water, indicates that millennial climate variability also had a strong impact on the eastern Mediterranean. The detailed analysis of the benthic δ13C and the fine sand content in the sediments from site U1389 led us to recognize the response of the Mediterranean overflow water (MOW) to millennial scale changes in Mediterranean overturning circulation during the penultimate glaciation. Both Mediterranean Overturning Circulation and MOW strength increased at times of cool and arid climates and weakened during warm and more humid episodes, similar to what has been described for MIS3. The tuning of MOW weakening events occurring at times of precession minima with eastern Mediterranean sapropels and enhanced Asian monsoon allowed the elaboration of a new chronology for MIS6. It was compared with the Epica Dome C time scale, which was also based on the tuning of atmospheric δ18O with Asian Monsoons speleothem records.Mediterranean overturning during MIS6 was also strongly affected by freshwater perturbations occurring at times of insolation maxima, leading to the formation of the “glacial sapropel” S6. Two major drops in seawater δ18O centered at 175 and 150 ky were observed near the entrance of the Mediterranean that were related to meltwater released from the ice sheets, coinciding with periods of insolation maxima. The entry of this meltwater anomaly through the Strait of Gibraltar is clearly registered in the western and eastern Mediterranean, especially at the onset of sapropel S6, suggesting that it was a major component of the freshwater that initiated the buoyancy gain preceding deep water stagnation.

Evolution of Sea Surface Hydrology Along the Western Australian Margin Over the Past 450 kyr

AbstractWe collected a suite of core top samples during R/V Sonne Cruise SO257 in May 2017 along the southwestern front of the Indo‐Pacific Warm Pool (IPWP) to monitor the variability of Southern Hemisphere tropical and subtropical sea surface hydrology and to assess temperature and salinity reconstructions with data sets reflecting conditions in the post‐monsoonal season. In our core top samples, a steep increase in planktic δ18O, associated with a decrease in sea surface temperature (SST), indicates that the southwestern front of the IPWP is located between 23° and 24°S during austral fall. We additionally reconstructed SST, sea surface salinity ,and δ18O seawater (δ18Osw) over the last 450 kyr in two sediment successions located within and beyond the monsoonal rain belt. Our records show that SST was highly coherent and phase‐locked with atmospheric pCO2 during the last 450 kyr. The regional differences in the δ18Osw records reveal that the Western Australian Margin north of 15°S remained seasonally under the influence of IPWP water masses, even during glacials. The temporal variability in upper ocean hydrology along the Western Australian Margin is not directly coupled to local monsoonal precipitation, but is strongly affected by advective mixing of Indonesian Throughflow derived water masses.

Variability of the Indian Monsoon in the Andaman Sea Across the Miocene‐Pliocene Transition

AbstractWe reconstructed the variability of the Earth's strongest hydrological system, the Indian monsoon, over the interval 6.24 to 4.91 Ma at International Ocean Discovery Program (IODP) Expedition 353 Site U1448 in the Andaman Sea. We integrated high‐resolution benthic and planktic foraminiferal carbon and oxygen isotopes with Mg/Ca measurements of the mixed layer foraminifer Trilobatus sacculifer to reconstruct the isotopic composition of seawater (δ18Osw) and the gradient between planktic and benthic foraminiferal δ13C. A prominent increase in mixed layer temperatures of ~4°C occurred between 5.55 and 5.28 Ma, accompanied by a change from precession‐ to obliquity‐driven variability in planktic δ18O and δ18Osw. We suggest that an intensified cross‐equatorial transport of heat and moisture, paced by obliquity, led to increased summer monsoon precipitation during warm stages after 5.55 Ma. Transient cold stages were characterized by reduced mixed layer temperatures and summer monsoon failure, thus resembling late Pleistocene stadials. In contrast, an overall cooler background climate state with a strengthened biological pump prevailed prior to 5.55 Ma. These findings highlight the importance of internal feedback processes for the long‐term evolution of the Indian monsoon.

Low‐frequency Pliocene climate variability in the eastern Nordic Seas

AbstractThe Pliocene (5.3–2.6 Ma) is often described as a relatively stable climatic period, with warm temperatures characterizing high latitudes. New suborbital resolved stable isotope records from Ocean Drilling Program Hole 642B in the eastern Nordic Seas document that the Pliocene was not a stable period characterized by one climate. Rather, seven distinct climate phases, each lasting between 150,000 and 400,000 years, are identified and characterized in the time interval 5.1–3.1 Ma. Four of the transitions between the defined climate phases occurred close to an eccentricity minimum and a minimum in amplitude of change for Northern Hemisphere summer insolation, while two occurred around an eccentricity maximum and a maximum in amplitude in insolation change. Hence, a low‐frequency response of the Nordic Seas to insolation forcing is indicated. In addition, paleogeographic and related paleoceanographic changes, expansion of the Arctic sea ice cover, and onset of Northern Hemisphere glaciation were important factors behind the evolving Pliocene low‐frequency variability in the eastern Nordic Seas. It is likely that the identified climate phases and transitions are important beyond the Nordic Seas, due to their association with changes to both insolation and paleogeography. However, a strong and variable degree of diagenetic calcite overgrowth is documented for the planktic foraminifera, especially influencing the planktic δ18O results; the absolute values and amplitude of change cannot be taken at face value.

Monsoon influence on planktic δ18O records from the South China Sea

While the benthic δ18O records from many South China Sea sites mimic the SPECMAP/LR04 standard, their paired planktic δ18O curves differ by comparable values at negative peaks corresponding to interstadials, especially between MIS 5.1, 5.3, 5.5, 6.5, and 7.3. Similar planktic δ18O records also occur in some other low-latitude oceans under monsoon influence. Because neither temperature nor salinity effects can fully account for the variations of such δ18O records after derivation from the SPECMAP/LR04 standard, variations in the rain water δ18O affected by regional hydroclimate changes are considered to have played an important role. In contrast to the SPECMAP/LR04 standard δ18O curve prevailed by 100-kyr cycles, these regional planktic δ18O curves are distinguished by 20-kyr precession signal, showing partial similarity to the δ18O records of atmospheric oxygen in polar ice-core bubbles and in stalagmite calcite. We speculate that the common features of these three independent δ18O records are indicative of the effect of evolving hydrological cycling driven by monsoon circulation in low latitudes.

Early deglacial onset of southwestern Greenland ice-sheet retreat on the continental shelf

The Greenland ice sheet (GrIS) advanced onto the continental shelf during the last glacial period. While deglacial records for when the GrIS withdrew onto the modern coastline are relatively abundant, the timing of early GrIS retreat on the shelf is poorly constrained. Here we use planktic foraminiferal δ18O, sediment grain size, sedimentation rates, and 14C ages in southeastern Davis Strait core HU87033-008 to develop an early deglaciation chronology of the southwestern GrIS while on the continental shelf. Sedimentation rates, and especially silt and clay fractions, are high between ∼20.5 and ∼17.1 ka, suggesting that the southwestern GrIS margin was near or at the shelf break, where it released subglacially derived sediment-laden meltwater. A peak in sedimentation rates of ∼110 cm ka−1 between ∼19.3 ka and ∼18.6 ka, combined with an initial decrease in planktic δ18O of ∼0.5 per mil, suggests an early deglacial pull back of the GrIS margin from the shelf break with a concurrent increase in surface ocean meltwater discharge. A subsequent planktic δ18O decrease of ∼1.0 per mil combined with a drop in silt and clay sedimentation rates at 18–17 ka likely record further GrIS retreat inland from the shelf break. Terrestrial 10Be surface exposure ages indicate that the GrIS margin remained on the continental shelf until ∼11 ka, yet the cause of this subsequent ice-margin stability on the inner shelf is not known. Our new records provide the first evidence that the southwestern GrIS margin may have begun to deglaciate at the same time as other Northern Hemisphere ice sheets. As Labrador Sea water temperatures likely remained near glacial values until ∼15 ka, we suggest that initial southwestern GrIS retreat was in response to rising global sea level from retreat of other ice sheets and/or the initial deglacial rise in boreal summer insolation.

Offset timing of climate oscillations during the last two glacial‐interglacial transitions connected with large‐scale freshwater perturbation

AbstractMultidecadal to centennial planktic δ18O and Mg/Ca records were generated at Ocean Drilling Program Site 976 (ODP976) in the Alboran Sea. The site is in the flow path of Atlantic inflow waters entering the Mediterranean and captured North Atlantic signals through the surface inflow and the atmosphere. The records reveal similar climatic oscillations during the last two glacial‐to‐interglacial transitions, albeit with a different temporal pacing. Glacial termination 1 (T1) was marked by Heinrich event 1 (H1), post‐H1 Bølling/Allerød warming, and Younger Dryas (YD) cooling. During T2 the H11 δ18O anomaly was twice as high and lasted 30% longer than during H1. The post‐H11 warming marked the start of MIS5e while the subsequent YD‐style cooling occurred during early MIS5e. The post‐H11 temperature increase at ODP976 matched the sudden Asian Monsoon Termination II at 129 ka B.P. Extending the 230Th‐dated speleothem timescale to ODP976 suggests glacial conditions in the Northeast Atlantic region were terminated abruptly and interglacial warmth was reached in less than a millennium. The early‐MIS5e cooling and freshening at ODP976 coincided with similar changes at North Atlantic sites suggesting this was a basin‐wide event. By analogy with T1, we argue that this was a YD‐type event that was shifted into the early stages of the last interglacial period. This scenario is consistent with evidence from northern North Atlantic and Nordic Sea sites that the continuing disintegration of the large Saalian Stage (MIS6) ice sheet in Eurasia delayed the advection of warm North Atlantic waters and full‐strength convective overturn until later stages of MIS5e.

Stratigraphic gaps at northern South China Sea margin reflect changes in Pacific deepwater inflow at glacial Termination II

To constrain short-term changes of climate and oceanography in the northern South China Sea (SCS) over interglacial marine isotope stage (MIS) 5.5, we studied planktic and benthic δ 18O records of seven marine sediment cores with a time resolution of 70–700 yr. Using 6-8 tie points the planktic records were tuned to the U/Th chronology of speleothem δ 18O records in China and Europe. The last occurrence of pink Globigerinoides ruber marks the top of Heinrich stadial 11 (HS-11) near 128.4 ka. HS-11 matches a 2300-yr long positive δ 18O excursion by 1.5/0.8‰ both in planktic and benthic δ18O records. Hence half of the planktic δ18O signal was linked to increased upwelling of 18O- and 12C-enriched deep waters in the southwestern SCS. The increase was possibly linked to a strengthened inflow of Pacific deep waters through the Bashi Strait, that form a boundary current along the northern slope of the SCS, building a major sediment drift. At its lower margin near 2300–2400 m water depth (w.d.) Parasound records reveal a belt of modern erosion. At the end of glacial termination 2, stratigraphic gaps deleted HS-11 in core MD05-2904 and subsequent peak MIS 5.5 at ODP Site 1144. Likewise hiatuses probably earmarked all preceding glacial terminations at Site 1144 back to 650 ka. Accordingly, boundary current erosion then shifted ∼300 m upslope to ∼2040–2060 m w.d. These vertical shifts imply a rise in boundary current buoyancy, that in turn may be linked to transient events of North Pacific deepwater formation similar to that traced in SCS and North Pacific paleoceanographic records over glacial termination 1.

Biogenic magnetite, detrital hematite, and relative paleointensity in Quaternary sediments from the Southwest Iberian Margin

Magnetic properties of late Quaternary sediments on the SW Iberian Margin are dominated by bacterial magnetite, observed by transmission electron microscopy (TEM), with contributions from detrital titanomagnetite and hematite. Reactive hematite, together with low organic matter concentrations and the lack of sulfate reduction, lead to dissimilatory iron reduction and availability of Fe(II) for abundant magnetotactic bacteria. Magnetite grain-size proxies (κARM/κ and ARM/IRM) and S-ratios (sensitive to hematite) vary on stadial/interstadial timescales, contain orbital power, and mimic planktic δ18O. The detrital/biogenic magnetite ratio and hematite concentration are greater during stadials and glacial isotopic stages, reflecting increased detrital (magnetite) input during times of lowered sea level, coinciding with atmospheric conditions favoring hematitic dust supply. Magnetic susceptibility, on the other hand, has a very different response being sensitive to coarse detrital multidomain (MD) magnetite associated with ice-rafted debris (IRD). High susceptibility and/or magnetic grain-size coarsening, mark Heinrich stadials (HS), particularly HS2, HS3, HS4, HS5, HS6 and HS7, as well as older Heinrich-like detrital layers, indicating the sensitivity of this region to fluctuations in the position of the polar front. Relative paleointensity (RPI) records have well-constrained age models based on planktic δ18O correlation to ice-core chronologies, however, they differ from reference records (e.g. PISO) particularly in the vicinity of glacial maxima, mainly due to inefficient normalization of RPI records in intervals of enhanced hematite input.

Millennial-scale climate variability during the mid-Pleistocene transition period in the northern South China Sea

Stable isotopes of foraminiferal multispecies (surface dwelling Globigerinoides ruber, thermocline dwelling Pulleniatina obliquiloculata, and benthic Uvigerina peregrina) and Mg/Ca ratios of G. ruber shells were analyzed with an average time resolution of ∼370 yr for reconstructing the orbital- and millennial-scale changes in the East Asian monsoon and associated upper water structure during the mid-Pleistocene period of 800–1060 ka at ODP Site 1144 in the northern South China Sea (SCS). It has been found that generally the sea surface temperature (SST) were lower and the depth of thermocline (DOT) was deeper during glacial stages and vice versa during interglacial stages, indicating a strengthened winter monsoon and weakened summer monsoon during glacial stages. The sea surface salinity (SSS) was relatively lower during glacials, induced by the greatly reduced distance of this site to the shore during times of low sea level. Further, spectral analyses have revealed significant semi-precessional and/or precessional cycles in the planktic δ18O, SST and the proxies of SSS and DOT, showing the typical characteristics of tropical climate change. This means that during the mid-Pleistocene climate transition (MPT) period the East Asian monsoon evolution and associated changes of upper water column structure in the northern SCS were probably driven partly by tropical forcing, like in the southern SCS, and should not be related only to the high latitude ice sheet changes. Particularly, millennial-scale climate fluctuations (mainly ∼1.4 kyr cycle) were found to exist throughout the glacial and interglacial stages during the MPT period in the northern SCS, but slightly different from the sawtooth-like D/O events recorded in late Quaternary Greenland ice cores. During the mid-Pleistocene terminations, the SST warming was synchronous with the northern ice sheet retreat, indicated by benthic δ18O, in the northern SCS, which is consistent to the previous findings in the late Quaternary SCS and apparently different from that in the western equatorial Pacific Ocean, providing new insights into the studies of East Asian monsoon evolution and rapid climate change.

Surface and deep water variations in the northeast Indian Ocean during 34–6 ka BP: Evidence from carbon and oxygen isotopes of fossil foraminifera

δ13C and δ18O records from planktic (Globigerinoides ruber) and benthic foraminifera (Cibicides spp.) were obtained from a deep sea sediment core (SK157–18) collected in the central Bay of Bengal. The chronology of this gravity core (11°59′N; 90°01′E; water-depth 3069 m; core-length 230 cm) has been established using six radiocarbon ages. Large variations in carbon and oxygen isotopes are suggestive of significant changes in surface and deep water of the Bay of Bengal during 34–6 ka BP. Planktic δ18O values in core SK157–18 are significantly higher compared to cores in the western Bay of Bengal and the Andaman Sea. A marked δ18O decrease at 8–7 ka BP is suggestive of low-salinity surface water in the central Bay of Bengal, probably due to the intensification of the Indian southwest monsoon (ISM). An increasing δ13C trend in G. ruber is seen during ∼34–26 and 14–7 ka BP and decreasing δ13C trend between 26 and 15 ka BP intervals. However these δ13C shifts in planktic foraminifera are not coherent with the glacial–interglacial change and may have been caused by wind-induced variability in surface water δ13C.The δ18O and δ13C values in benthic foraminifera show considerable variations during the Holocene and glacial times. Last Glacial Maximum (LGM) to Holocene δ18O shift in benthic foraminifera (1.5‰) exceeds ice volume effect by ∼0.5‰, suggesting glacial deep water cooling of ∼2 °C, assuming no salinity change. This glacial deep water cooling may have been caused by the introduction of cooler Southern Ocean Deep Water (SODW). Large fluctuations in benthic δ13C are due to the changes in source water characteristics during the Holocene and last glaciation. Glacial benthic foraminifera exhibit pronounced decrease in δ13C suggesting reduced contribution from the North Atlantic Deep Water (NADW) and increased influx of SODW. In addition, oxidation of organic matter due to the reduced ventilation of deep water masses during the LGM may have contributed in the significant decrease in δ13C.

Antarctic Isotope Maxima events 24 and 25 identified in benthic marine δ18O

High‐resolution planktic and benthic δ18O records at Site 1146 (northern South China Sea) include structure within Marine Isotope Stage 5.4, 118.5–105.9 ka, that is not captured in stacked δ18O records commonly used for age model construction and as proxies for global ice volume. Leveraging a common monsoonal influence, Site 1146 planktic δ18O was aligned to speleothem δ18O from southeastern China to derive a radiometrically calibrated (RC) age model. On the RC age model, the benthic δ18O record contains structure equivalent in time to Antarctic Isotope Maximum (AIM) events 24 and 25. Sea level reconstructions for isotopic event 5.4 suggest that these benthic δ18O events (AIM 24 and 25) derive from isotopic change (ice volume) although some temperature change cannot be completely excluded.

Short-term warming events during the boreal Albian (mid‑Cretaceous)

Research Article| March 01, 2011 Short-term warming events during the boreal Albian (mid‑Cretaceous) Jochen Erbacher; Jochen Erbacher 1Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany Search for other works by this author on: GSW Google Scholar Oliver Friedrich; Oliver Friedrich 2National Oceanography Centre Southampton, University of Southampton, European Way, Southampton SO14 3ZH, UK3Institute of Geosciences, Goethe-University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany Search for other works by this author on: GSW Google Scholar Paul A. Wilson; Paul A. Wilson 2National Oceanography Centre Southampton, University of Southampton, European Way, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Jens Lehmann; Jens Lehmann 4Faculty of Geosciences, University of Bremen, Klagenfurter Strasse, 28357 Bremen, Germany Search for other works by this author on: GSW Google Scholar Wolfgang Weiss Wolfgang Weiss 1Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Jochen Erbacher 1Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany Oliver Friedrich 2National Oceanography Centre Southampton, University of Southampton, European Way, Southampton SO14 3ZH, UK3Institute of Geosciences, Goethe-University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany Paul A. Wilson 2National Oceanography Centre Southampton, University of Southampton, European Way, Southampton SO14 3ZH, UK Jens Lehmann 4Faculty of Geosciences, University of Bremen, Klagenfurter Strasse, 28357 Bremen, Germany Wolfgang Weiss 1Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany Publisher: Geological Society of America Received: 23 Jul 2010 Revision Received: 01 Oct 2010 Accepted: 06 Oct 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (3): 223–226. https://doi.org/10.1130/G31606.1 Article history Received: 23 Jul 2010 Revision Received: 01 Oct 2010 Accepted: 06 Oct 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jochen Erbacher, Oliver Friedrich, Paul A. Wilson, Jens Lehmann, Wolfgang Weiss; Short-term warming events during the boreal Albian (mid‑Cretaceous). Geology 2011;; 39 (3): 223–226. doi: https://doi.org/10.1130/G31606.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Pronounced paleotemperature variations associated with the carbon cycle perturbations of oceanic anoxic events (OAEs 1b and 1d) are known to have occurred during the early and latest Albian. However, reliable paleotemperature data spanning the 12 m.y. between these two events are sparse. Here we present δ18O, δ13C, and Mg/Ca data for the middle to early-late Albian based on analysis of unusually well preserved “glassy” foraminifers from a clay-rich sequence drilled in the boreal Lower Saxony Basin (northwestern Germany; ∼45°N paleolatitude). Our records reveal pronounced variability in planktic δ18O (∼1.5‰–2.5‰) on a 100 k.y. time scale that we interpret to indicate substantial changes in sea-surface temperature (to ∼7 °C) and δ18O/salinity (to ∼3 psu). Our findings attest to the climatic sensitivity of marginal basins in these boreal latitudes during the mid-Cretaceous and suggest that the heat and salt budgets of the Lower Saxony Basin were orbitally conditioned during the Albian, presumably through atmospheric or oceanic heat transport from lower latitudes where surface waters were warmer than today, in response to strong greenhouse gas forcing. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Reconstruction of deep-water conditions in the North Atlantic during MIS 9 based on benthic foraminiferal assemblages

Marine isotope stage (MIS) 9 is one of the least investigated Pleistocene interglaciations. The present study describes reconstructions of deep-water conditions during this time interval based on benthic foraminiferal assemblages from sediment core M23414 (Rockall Plateau, North Atlantic). The results of faunal analysis were supported by planktic δ18O, sea surface temperature reconstructions based on planktic foraminiferal assemblages and content of ice rafted debris. Statistical data processing using principal component analysis revealed five climate-related benthic foraminiferal associations that changed in response to alterations of deep-water circulation.

Sea ice and marine climate variability for NW Iceland/Denmark Strait over the last 2000 cal. yr BP

MD99-2263 is a 46 cm box core collected from Djupall, a trough that cuts across the NW Iceland Shelf and ends above Denmark Strait. We provide a multiproxy record that documents changes in the regional marine climate over the last ~1700 yr. The depth/age model is based on seven calibrated radiocarbon dates on mollusk shells and on 210Pb and 137Cs. Sediment accumulation rates were variable (0.2—0.8 mm/yr) but increased dramatically ~AD 1500. Grain-size, magnetic properties, quantitative mineral composition of the <2 mm sediment fraction, benthic foraminiferal composition, benthic and planktic Δ18O ratios, and abundances/fluxes of the sea ice biomarker IP25 were determined. To better compare the various proxies, 12 of the critical climate proxies were co-ordinated into 100-yr/sample time series, which were examined by Principal Component Analysis. The 1st axis explained 49% of the variance and the 2nd axis explained an additional 17%. The variables most strongly associated with the 1st axis were sediment properties (phi mean, clay%) and the sea ice biomarker. Mineralogical indicators of drift ice rafting, such as the presence of quartz and potassium- and sodium-feldspars, coincide with the IP25 biomarker data and show an increase after AD 1200, but high values of quartz and some feldspars also occurred between c. AD 300 and 900 with pronounced minima between AD 900 and 1100. Overall, our data suggest a simple two-fold division in climate conditions over the last 1700 yr, with the major change occurring c. AD 1200. In the last few decades, conditions have reverted towards those experienced prior to AD 1200.

Early Maastrichtian carbon cycle perturbation and cooling event: Implications from the South Atlantic Ocean

Published stable isotope records in marine carbonate are characterized by a positive δ18O excursion associated with a negative δ13C shift during the early Maastrichtian. However, the cause and even the precise timing of these excursions remain uncertain. We have generated high‐resolution foraminiferal stable isotope and gray‐scale records for the latest Campanian to early Maastrichtian (∼73–68 Ma) at two Ocean Drilling Program sites, 525 (Walvis Ridge) and 690 (Weddell Sea). We demonstrate that the negative δ13C excursion is decoupled from the δ18O increase with a lag of about 600 ka. Our δ13C records (both planktic and benthic) show an amplitude for the negative excursion of 0.7‰ that falls between about 72.1 and 70.7 Ma. Our planktic δ18O records indicate an overall increase of 1.2‰ from 73 to 68 Ma at Site 690, whereas at Site 525 they record a slightly smaller increase (∼1‰) that peaks around 70.1 Ma with decreasing values thereafter. Our benthic δ18O data indicate an increase of ∼1.5‰ at Site 525 and ∼0.7‰ at Site 690 between about 71.4 and 69.9 Ma. Benthic δ18O values show different baseline values at the two sites before and after the excursion, but the larger increase at Site 525 means that the values attained at the peak of the excursion are similar at the two sites. We interpret this observation in terms of water mass changes. The excursion is interpreted to reflect a cooling of bottom waters in response to the strengthening contribution of intermediate‐ to deep‐water production in the high southern latitudes rather than increased ice volume. The associated carbon cycle perturbations that we observe are interpreted to reflect a weakening of surface water stratification and increased productivity, as supported by our gray value data.