Temporal variation of temperature and related proxies from the penultimate glacial towards the Eemian in the Black Sea

The last glacial-interglacial transition or Termination I (T I) is well documented in the Black Sea, whereas little is known about climate and environmental dynamics during the penultimate Termination (T II). Here we present a multi-proxy study based on a sediment core from the SE Black Sea covering the penultimate glacial and almost the entire Eemian interglacial (133.5 ±0.7-122.5 ±1.7 ka BP). Proxies comprise ice-rafted debris (IRD), O and Sr isotopes as well as Sr/Ca, Mg/Ca, and U/Ca ratios of benthic ostracods, organic and inorganic sediment geochemistry, as well as TEX86 and UK'37derived water temperatures. The ending penultimate glacial (MIS 6, 133.5 to 129.9 ±0.7 ka BP) is characterised by mean annual lake surface temperatures of about 9°C as estimated from the TEX86 palaeothermometer. This period is impacted by two Black Sea melt water pulses (BSWP-II-1 and 2) as indicated by very low Sr/Ca ostracods but high sedimentary K/Al values. Anomalously high radiogenic 87Sr/86Sr ostracod values (max. 0.70945) during BSWP-II-2 suggest a potential Himalayan source communicated via the Caspian Sea. The T II warming started at 129.9 ±0.7 ka BP, witnessed by abrupt disappearance of IRD, increasing d18O ostracod values, and a first TEX86 derived temperature rise of about 2.5°C. A second, abrupt warming step to ca. 15.5°C as the prelude of the Eemian warm period is documented at 128.3 ka BP. The Mediterranean-Black Sea reconnection most likely occurred at 128.1 ±0.7 ka BP as demonstrated by increasing Sr/Ca ostracods and U/Ca ostracods values. The disappearance of ostracods and TOC contents >2% document the onset of Eemian sapropel formation at 127.6 ka BP. During sapropel formation, TEX86 temperatures dropped and stabilised at around 9°C, while UK'37 temperatures remain on average 17°C. This difference is possibly caused by a habitat shift of Thaumarchaeota communities from surface towards nutrient-rich deeper and colder waters located above the gradually establishing halo-and redoxcline.

(Table 1) Age determination of sediment core BC5, Golf of Lion

Hitherto unknown abundance peaks of left coiling (l.c.) Neogloboquadrina pachyderma from a Gulf of Lions piston core indicate that abrupt cold spells associated with Atlantic Heinrich events affected the Mediterranean. N. pachyderma (l.c.) is typical of (sub) polar waters in the open ocean. The southern edge of its glacial North Atlantic bioprovince reached south Portugal. Only trace abundances of N. pachyderma (l.c.) are known from Quaternary Mediterranean sediments, suggesting that no significant "invasions" occured via the Strait of Gibraltar. The Gulf of Lions abundance peaks therefore seem to reflect area-specific thriving of a normally rare but indigenous taxon in the western Mediterranean through local favorable habitat development. The general planktonic foraminiferal record suggests that the basic hydrographic regime in the Gulf of Lions, with wintertime deep convective overturn, was relatively stable over the past 60 kyr. Under these conditions, high abundances of N. pachyderma (l.c.) would essentially imply temperature reductions of the order of 5°-8° relative to the present.

Grain-size, lithic grains, foraminifera-derived and dinocyst-derived data of sediment core MD99-2281

The last glacial period was punctuated by abrupt climatic events with extrema known as Heinrich and Dansgaard-Oeschger events. These millennial events have been the subject of many paleoreconstructions and model experiments in the past decades, but yet the hydrological processes involved remain elusive. In the present work, high-resolution analyses were conducted on the 12-42 ka BP section of core MD99-2281 retrieved southwest of the Faeroe Islands, and combined with analyses conducted in two previous studies (Zumaque et al., 2012; Caulle et al., 2013). Such a multiproxy approach, coupling micropaleontological, geochemical and sedimentological analyses, allows us to track surface, subsurface, and deep hydrological processes occurring during these rapid climatic changes. Records indicate that the coldest episodes of the studied period (Greenland stadials and Heinrich stadials) were characterized by a strong stratification of surface waters. This surface stratification seems to have played a key role in the dynamics of subsurface and deep-water masses. Indeed, periods of high surface stratification are marked by a coupling of subsurface and deep circulations which sharply weaken at the beginning of stadials, while surface conditions progressively deteriorate throughout these cold episodes; conversely, periods of decreasing surface stratification (Greenland interstadials) are characterized by a coupling of surface and deep hydrological processes, with progressively milder surface conditions and gradual intensification of the deep circulation, while the vigor of the subsurface northward Atlantic flow remains constantly high. Our results also reveal different and atypical hydrological signatures during Heinrich stadials (HSs): while HS1 and HS4 exhibit a "usual" scheme with reduced overturning circulation, a relatively active North Atlantic circulation seems to have prevailed during HS2, and HS3 seems to have experienced a re-intensification of this circulation during the middle of the event. Our findings thus bring valuable information to better understand hydrological processes occurring in a key area during the abrupt climatic shifts of the last glacial period.

(Table T1) Initial water quality conditions for bioassay experiments during Nathaniel B. Palmer cruise NBP09-01 in the Amundsen Sea

Nutrient addition experiments were performed during the austral summer in the Amundsen Sea (Southern Ocean) to investigate the availability of organically bound iron (Fe) to the phytoplankton communities, as well as assess their response to Fe amendment. Changes in autotrophic biomass, pigment concentration, maximum photochemical efficiency of photosystem II, and nutrient concentration were recorded in response to the addition of dissolved free Fe (DFe) and Fe bound to different model ligands. Analysis of pigment concentrations indicated that the autotrophic community was dominated by the prymnesiophyte Phaeocystis antarctica throughout most of the Amundsen Sea, although diatoms dominated in two experiments conducted in the marginal ice zone. Few significant differences in bulk community biomass (particulate organic carbon, nitrogen, and chlorophyll a) were observed, relative to the controls, in treatments with Fe added alone or bound to the ligand phytic acid. In contrast, when Fe was bound to the ligand desferrioxamine B (DFB), decreases in the bulk biomass indices were observed. The concentration of the diatom accessory pigment fucoxanthin showed little response to Fe additions, while the concentration of the P. antarctica-specific pigment, 19'-hexanoyloxyfucoxanthin (19'-hex), decreased when Fe was added alone or bound to the model ligands. Lastly, differences in the nitrate:phosphate (NO3- :PO4**3-) utilization ratio were observed between the Fe-amended treatments, with Fe bound to DFB resulting in the lowest NO3- :PO4**3- uptake ratios (~ 10) and the remaining Fe treatments having higher NO3- :PO4**3- uptake ratios (~ 17). The data are discussed with respect to glacial inputs of Fe in the Amundsen Sea and the bioavailability of Fe. We suggest that the previously observed high NO3- :PO4**3- utilization ratio of P. antarctica is a consequence of its production of dissolved organic matter that acts as ligands and increases the bioavailability of Fe, thereby stimulating the uptake of NO3-.

Age determination of sediment core GIK16523-1

High-resolution studies of a planktonic foraminifer core record from the South China Sea (SCS) (31KL: 18°45.4'N, 115°52.4'E, water depth 3360 m) reveal changes driven by ice-volume forcings in the climate of the East Asian monsoon in the western Pacific marginal sea during the late Quaternary. The analyses of planktonic foraminifer faunal abundance data from the core indicate significant variations in the relative abundances of the dominant taxa over the past 100,000 years since the isotope stage 5. The transfer function estimates of faunal sea surface temperatures (SST) correlate well with a long-term (104-105 years) trend of global glaciation. About 65,000 years ago, there was an observable change in the mode of SST variability as many low-latitude records have shown. These findings suggest that the SCS surface circulation and the East Asian winter monsoon systems are mainly driven by variations in global glaciation levels. The association of surface ocean cooling in the SCS with global climatic events suggests that fluctuations in the strength of the East Asian winter monsoon may be linked to shifts in the latitudinal position of the westerly winds and the Siberian high-pressure system.

(Table 1) Age control and temporal resolution of paleoceanographic records of the North Atlantic

Short-term changes in sea surface conditions controlling the thermohaline circulation in the northern North Atlantic are expected to be especially efficient in perturbing global climate stability. Here we assess past variability of sea surface temperature (SST) in the northeast Atlantic and Norwegian Sea during Marine Isotope Stage (MIS) 2 and, in particular, during the Last Glacial Maximum (LGM). Five high-resolution SST records were established on a meridional transect (53°N-72°N) to trace centennial-scale oscillations in SST and sea-ice cover. We used three independent computational techniques (SIMMAX modern analogue technique, Artificial Neural Networks (ANN), and Revised Analog Method (RAM)) to reconstruct SST from planktonic foraminifer census counts. SIMMAX and ANN reproduced short-term SST oscillations of similar magnitude and absolute levels, while RAM, owing to a restrictive analog selection, appears less suitable for reconstructing "cold end" SST. The SIMMAX and ANN SST reconstructions support the existence of a weak paleo-Norwegian Current during Dansgaard-Oeschger (DO) interstadials number 4, 3, 2, and 1. During the LGM, two warm incursions of 7°C water to occurred in the northern North Atlantic but ended north of the Iceland Faroe Ridge. A rough numerical estimate shows that the near-surface poleward heat transfer from 53° across the Iceland-Faroe Ridge up to to 72° N dropped to less than 60% of the modern value during DO interstadials and to almost zero during DO stadials. Summer sea ice was generally confined to the area north of 70°N and only rarely expanded southward along the margins of continental ice sheets. Internal LGM variability of North Atlantic (>40°N) SST in the GLAMAP 2000 compilation (Sarnthein et al., 2003, doi:10.1029/2002PA000771; Pflaumann et al., 2003, doi:10.1029/2002PA000774) indicates maximum instability in the glacial subpolar gyre and at the Iberian Margin, while in the Nordic Seas, SST was continuously low.

Oxygen isotopic measurements from Holcene of sediment core MD02-2529, tropical pacific

Changes in El Niño-Southern Oscillation (ENSO) variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first-order climate signal. Here we address this problem by reconstructing thermocline structure from a marine sediment core retrieved from the eastern equatorial Pacific. At the core location, changes in hydrologic parameters within the thermocline are linked to ENSO activity, with a reduced influence of seasonal variability compared to surface waters. We performed repeated isotopic analyses (d18O) on single specimens of the thermocline-dwelling planktonic foraminifera Neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance, a parameter supposed to reveal changes in ENSO. No fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background. However, our data suggest that long-term variations in the thermocline variability occurred over the last 50 ka, with the highest and lowest ENSO activities occurring during the last glacial period and the Last Glacial Maximum, respectively.

(Table S2) The reconstructed sea surface temperature (SST) over the eastern equatorial Pacific

Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18-15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5-1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.