ALBERT

Description: Planktic foraminiferal census data, faunal sea surface temperatures (SSTs) and oxygen isotopic and lithic records from a site in the northeast Atlantic were analyzed to study the interglacial dynamics of Marine Isotope Stage (MIS) 11, a period thought to closely resemble the Holocene on the basis of orbital forcing. Interglacial conditions during MIS 11 persisted for approximately 26 ka. After the main deglacial meltwater processes ceased, a 10- to 12-ka-long transitional period marked by significant water mass circulation changes occurred before surface waters finally reached their thermal maximum. This SST peak occurred between 400 and 397 ka, inferred from the abundance of the most thermophilic foraminiferal species and was coincident with lowest sea level according to benthic isotope values. The ensuing stepwise SST decrease characterizes the overall climate deterioration preceding the increase in global ice volume by ∼ 3 ka. This cooling trend was followed by a more pronounced cold event that began at 388 ka, and that terminated in the recurrence of icebergs at the site around 382 ka. Because the water mass configuration of early MIS 11 evolved quite differently from that of the early Holocene, there is little evidence that MIS 11 can serve as an appropriate analogue for a future Holocene climate, despite the similarity in some orbital parameters.

Description: Climate variability in the northeast Atlantic was investigated on glacial–interglacial and millennial time scales during the last 200 000 years, using sea surface temperature (SST) records derived from planktonic foraminiferal diversities and from Mg/Ca measurements on Globigerina bulloides. Paleoceanographical interpretations are supported by species composition analyses, benthic and planktonic isotopic data as well as records of iceberg-rafted debris (IRD). Differences of climate development are recognized for both interglacial and glacial periods. Temperature estimates indicate slightly warmer conditions (up to 2°C) during marine oxygen isotope stage (MIS) 5e than during the Holocene. In contrast to the last glaciation, when the SST minimum coincided with a minimum in solar insolation immediately before Termination I, during the penultimate glaciation a long SST minimum occurred at times of intermediate solar insolation well preceding the onset of Termination II. This discrepancy between two glacial terminations may be explained by an inherently different orbital configuration characteristic for each glacial interval. Despite these differences between the two glacial trends, the superimposed shorter-lived climatic events reveal the same order of principal steps, implying their common causal nature. A direct comparison of faunal SSTs with those retrieved from Mg/Ca analysis shows that Mg/Ca-derived temperatures follow the general glacial–interglacial trend; however, the latter appear to be largely overestimated. Supported by δ18O data in G. bulloides, which show little response to millennial-scale variability, there seems to be a need for species-dependent calibration experiments that also consider the different oceanographic settings this particular species can live in.

Description: Highlights • Climate progression in the Balearic basin is examined between 140 and 100 ka. • A number of MIS 5e intra-interglacial cooling events is recognized. • MIS 5e climate phasing in the Western Mediterranean resembles the one in the Nordic Seas. • Foraminiferal abundances are strongly tied to a water circulation regime. • The timing of ORL deposition during MIS 5e resembles that of during the Holocene. Abstract A multiproxy analysis based on planktic foraminiferal abundances, derived SSTs, and stable planktic isotopes measurements together with alkenone abundances and Uk′37 SSTs was performed on late MIS 6 to early MIS 5d sediment recovered from Site 975 (ODP Leg 161) in the South Balearic Islands Basin (Western Mediterranean) with emphasis on reconstructing the climate progression of the last interglacial period. A number of abrupt climate changes related to alternative influence of nutrient rich northern and oligotrophic southern water masses was revealed. Heinrich event 11 and cooling events C27, C26, C25, C24, and C23, which have been previously described in the North Atlantic, were recognized. However, in comparison to the eastern North Atlantic mid-latitude region, events C27 and C26 at Site 975 seem to be significantly more pronounced. Together with evidence of a two-phase climate optimum with maximum SSTs reached during its later phase, this implies a close similarity in climate dynamics between the Western Mediterranean and the Nordic seas. We propose that postglacial effects in the Nordic seas had an influence on the western Mediterranean climate via atmospheric circulation and that these effects competed with the insolation force.

Description: Highlights • Holocene sea subsurface temperatures after Husum & Hald (2012) estimated from planktic foraminifer fauna in E Fram Strait. • Biomarkers and IP25-derived indices (including DIP25) indicate surface water variability. • Delayed onset of early Holocene conditions in subsurface (∼10.6 ka) compared to surface (∼11.7 ka) water conditions. • Warm Atlantic layer likely occupied uppermost 200 m in eastern Fram Strait between 10 and 9 ka. • Diverging late Holocene trends in surface and subsurface conditions linked to presence of strong pycnocline/stratification. Abstract Two high-resolution sediment cores from eastern Fram Strait have been investigated for sea subsurface and surface temperature variability during the Holocene (the past ca 12,000 years). The transfer function developed by Husum and Hald (2012) has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period. Additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions, and to conclude on the Holocene climate and oceanographic variability on the West Spitsbergen continental margin. Results consistently reveal warm sea surface to subsurface temperatures of up to 6 °C until ca 5 cal ka BP, with maximum seawater temperatures around 10 cal ka BP, likely related to maximum July insolation occurring at that time. Maximum Atlantic Water (AW) advection occurred at surface and subsurface between 10.6 and 8.5 cal ka BP based on both foraminiferal and dinocyst temperature reconstructions. Probably, a less-stratified, ice-free, nutrient-rich surface ocean with strong AW advection prevailed in the eastern Fram Strait between 10 and 9 cal ka BP. Weakened AW contribution is found after ca 5 cal ka BP when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka BP. Cold late Holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high δ18O values of the subpolar planktic foraminifer species Turborotalita quinqueloba. While IP25-associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea-ice increase since about 7 cal ka BP in surface waters, planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface AW influx since ca 3 cal ka BP. The observed decoupling of surface and subsurface waters during the later Holocene is most likely attributed to a strong pycnocline layer separating cold sea-ice fed surface waters from enhanced subsurface AW advection. This may be related to changes in North Atlantic subpolar versus subtropical gyre activity.

Description: The deep and surface water paleoceanographic evolution of the central Nordic Seas over the last 20 thousand years was reconstructed using various micropaleontological, isotopic and lithological proxy data. These show a high spatial and temporal complexity of the oceanic circulation when compared with other records from the region. During early deglaciation a collapse of ice sheets surrounding the Nordic Seas released large amounts of freshwater that affected both the surface and bottom water circulation and significantly contributed to Heinrich stadial 1. During the Younger Dryas, the central Nordic Seas were affected by a last major freshwater plume which probably originated from the Arctic Ocean. When major ice rafting had ceased around 11ka subsurface temperatures started to rise. However, Atlantic Water advection and subsurface temperatures reached their maximum in the central Nordic Seas later than along the eastern continental margin. That spatio-temporal offset is explained by a gradual re-routing and westward expansion of the Atlantic Water flow during times when the Greenland Sea gyre system became more steadily established. In the Greenland Basin, the Holocene thermal maximum ended c. 5.5ka, and time-coeveal with an increase in sea-ice export from the Arctic. In the Lofoten Basin the cooling occurred later, after 4ka, and together with a weakening of the overturning processes. The Neoglacial cooling was reached c. 3ka, together with low solar irradiance, expanding sea ice and a slight decrease in deep convection. At c. 2ka subsurface temperatures began to rise again due to an increasing influence of Atlantic Waters.

Description: A multiproxy data set of an AMS radiocarbon dated 46 cm long sediment core from the continental margin off western Svalbard reveals multidecadal climatic variability during the past two millennia. Investigation of planktic and benthic stable isotopes, planktic foraminiferal fauna, and lithogenic parameters aims to unveil the Atlantic Water advection to the eastern Fram Strait by intensity, temperatures, and salinities. Atlantic Water has been continuously present at the site over the last 2,000 years. Superimposed on the increase in sea ice/icebergs, a strengthened intensity of Atlantic Water inflow and seasonal ice-free conditions were detected at ~ 1000 to 1200 AD, during the well-known Medieval Climate Anomaly (MCA). However, temperatures of the MCA never exceeded those of the 20th century. Since ~ 1400 AD significantly higher portions of ice rafted debris and high planktic foraminifer fluxes suggest that the site was located in the region of a seasonal highly fluctuating sea ice margin. A sharp reduction in planktic foraminifer fluxes around 800 AD and after 1730 AD indicates cool summer conditions with major influence of sea ice/icebergs. High amounts of the subpolar planktic foraminifer species Turborotalia quinqueloba in size fraction 150–250 μm indicate strengthened Atlantic Water inflow to the eastern Fram Strait already after ~ 1860 AD. Nevertheless surface conditions stayed cold well into the 20th century indicated by low planktic foraminiferal fluxes. Most likely at the beginning of the 20th century, cold conditions of the terminating Little Ice Age period persisted at the surface whereas warm and saline Atlantic Water already strengthened, hereby subsiding below the cold upper mixed layer. Surface sediments with high abundances of subpolar planktic foraminifers indicate a strong inflow of Atlantic Water providing seasonal ice-free conditions in the eastern Fram Strait during the last few decades.