Radiocarbon dates of sediments from ODP Site 161-976

Multiproxy paleoenvironmental records (pollen and planktonic isotope) from Ocean Drilling Program Site 976 (Alboran Sea) document rapid ocean and climate variations during the last glacial that follow the Dansgaard-Oeschger climate oscillations seen in the Greenland ice core records, thus suggesting a close link of the Mediterranean climate swings with North Atlantic climates. Continental conditions rapidly oscillated through cold-arid and warm-wet conditions in the course of stadial-interstadial climate jumps. At the time of Heinrich events, i.e., maximum meltwater flux to the North Atlantic, western Mediterranean marine microflora and microfauna show rapid cooling correlated with increasing continental dryness. Enhanced aridity conceivably points to prolonged wintertime stability of atmospheric high-pressure systems over the southwestern Mediterranean in conjunction with cooling of the North Atlantic.

High-resolution planktic stable isotope and trace element record of ODP Hole 161-976

Multi-decadal to centennial planktic d18O and Mg/Ca records were generated at 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 Bolling/Allerod (B/A) warming and Younger Dryas (YD) cooling. During T2 the H11 d18O 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 BP. 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.

(Table 1) Oxygen isotopic composition of interstitial waters from ODP Hole 161-976

Interstitial waters recovered from Ocean Drilling Program, Leg 161, site 976 in the western Mediterranean Sea are used in conjunction with a numerical model to constrain the delta18O of seawater in the basin since the Last Glacial Maximum, including Sapropel Event 1. To resolve the oxygen isotopic composition of the deep Mediterranean, we use a model that couples fluid diffusion with advective transport, thus producing a profile of seawater delta18O variability that is unaffected by glacial-interglacial variations in marine temperature. Comparing our reconstructed seawater delta18O to recent determinations of 1.0 per mil for the mean ocean change in glacial-interglacial delta18O due to the expansion of global ice volume, we calculate an additional 0.2 per mil increase in Mediterranean delta18O caused by local evaporative enrichment. This estimate of delta18O change, due to salinity variability, is smaller than previous studies have proposed and demonstrates that Mediterranean records of foraminiferal calcite delta18O from the last glacial period include a strong temperature component. Paleotemperatures determined in combination with a stacked record of foraminiferal calcite depict almost 9°C of regional cooling for the Last Glacial Maximum. Model results suggest a decrease of ~1.1 per mil in seawater delta18O relative to the modern value caused by increased freshwater input and reduced salinity accompanying the formation of the most recent sapropel. The results additionally indicate the existence of isotopically light water circulating down to bottom water depths, at least in the western Mediterranean, supporting the existence of an 'anti-estuarine' thermohaline circulation pattern during Sapropel Event 1.

Horizontal profiles of longwave and shortwave radiation components over sea ice near Barrow, Alaska during the 2011 melt

An integrated instrument package for measuring and understanding the surface radiation budget of sea ice is presented, along with results from its first deployment. The setup simultaneously measures broadband fluxes of upwelling and downwelling terrestrial and solar radiation (four components separately), spectral fluxes of incident and reflected solar radiation, and supporting data such as air temperature and humidity, surface temperature, and location (GPS), in addition to photographing the sky and observed surface during each measurement. The instruments are mounted on a small sled, allowing measurements of the radiation budget to be made at many locations in the study area to see the effect of small-scale surface processes on the large-scale radiation budget. Such observations have many applications, from calibration and validation of remote sensing products to improving our understanding of surface processes that affect atmosphere-snow-ice interactions and drive feedbacks, ultimately leading to the potential to improve climate modelling of ice-covered regions of the ocean. The photographs, spectral data, and other observations allow for improved analysis of the broadband data. An example of this is shown by using the observations made during a partly cloudy day, which show erratic variations due to passing clouds, and creating a careful estimate of what the radiation budget along the observed line would have been under uniform sky conditions, clear or overcast. Other data from the setup's first deployment, in June 2011 on fast ice near Point Barrow, Alaska, are also shown; these illustrate the rapid changes of the radiation budget during a cold period that led to refreezing and new snow well into the melt season.