Independent tephrochronological evidence for rapid and synchronous oceanic and atmospheric temperature rises over the Greenland stadial-interstadial transitions between ca. 32 and 40 ka b2k

Understanding the dynamics that drove past abrupt climate changes, such as the Dansgaard-Oeschger (DO) events, depends on combined proxy evidence from disparate archives. To identify leads, lags and synchronicity between different climate system components, independent and robust chronologies are required. Cryptotephrochronology is a key geochronological tool as cryptotephra horizons can act as isochrons linking disparate and/or distant records. Here, we investigated marine sediment core MD99-2284 from the Norwegian Sea to look for previously identified Greenland ice core cryptotephra horizons and define time-parallel markers between the archives. We explored potential secondary transport and depositional mechanisms that could hamper the isochronous integrity of such horizons. We identified six cryptotephra layers of which four correlate to previously known Greenland ice core horizons. None of those were identified in other marine cores and thus, this study contributes greatly to the North Atlantic tephra framework tripling the original amount of existing isochrons between ca. 25 and 60 ka b2k. The latter allow a synchronization between MD99-2284 and the Greenland ice cores between ca. 32 e40 ka b2k, which is, in the North Atlantic, the shortest time-interval during the Last Glacial Period to be constrained by four independent tephra isochrons. These findings provide essential tephra-based evidence for synchronous and rapid oceanic and atmospheric temperature rises during the Greenland Stadial-Interstadial transitions. Furthermore, it enables us to estimate the average peak-duration of interstadial temperature overshoots at approximately 136 years. As such, this well-targeted high-resolution investigation successfully demonstrates the use of cryptotephra for geochronological purposes in the marine realm.publishedVersio

Co-feeding of live feed and inert diet from first-feeding affects Artemia lipid digestibility and retention in Senegalese sole (Solea senegalensis) larvae

The present study intended to evaluate the effects of early introduction of inert diet in lipid digestibility and metabolism of sole, while larval feed intake, growth and survival were also monitored. Solea senegalensis larvae were reared on a standard live feed regime (ST) and co-feeding regime with inert diet (Art R). Trials using sole larvae fed with Artemia enriched with two different lipid emulsions, containing glycerol tri [1-14C] oleate (TAG) and L-3-phosphatidylcholine-1,2-di-[1-14C] oleoyl (PL), were performed at 9 and 17 days after hatching (DAH) to study lipid utilization. Co-feeding did not affect sole survival rates (ST 59.1 ± 15.9 %; Art R 69.56 ± 9.3 %), but was reflected in significantly smaller final weight at 16 DAH (ST 0.71 ± 0.20; Art R 0.48 ± 0.14 mg). Higher feed intake was observed in sole larvae fed on Artemia enriched with labeled PL at 9 DAH but not at 17 DAH. At 17 DAH, the smaller larvae (Art R treatment) ingested proportionally more Artemia in weight percentage, independently of enrichment. At 9 DAH lipid digestibility was equal among treatments and higher than 90%, while at 17 DAH it was higher in ST treatment (around 73 %) compared to the Art R group (around 66 %). Lipid retention efficiency at 9 DAH was higher in the Art R treatment, reaching values of 50 %, while these values almost duplicated at 17 DAH, ranging up to 80 % in both treatments without significant differences. These results show that co-feeding of live feed and inert diet from first-feeding in Senegalese sole has a toll in terms of growth and lipid digestibility but does not seem to compromise lipid metabolic utilization

Sea ice variability in the southern Norwegian Sea during glacial Dansgaard-Oeschger climate cycles.

The last glacial period was marked by pronounced millennial-scale variability in ocean circulation and global climate. Shifts in sea ice cover within the Nordic Seas are believed to have amplified the glacial climate variability in northern high latitudes and contributed to abrupt, high-amplitude temperature changes over Greenland. We present unprecedented empirical evidence that resolves the nature, timing, and role of sea ice fluctuations for abrupt ocean and climate change 32 to 40 thousand years ago, using biomarker sea ice reconstructions from the southern Norwegian Sea. Our results document that initial sea ice reductions at the core site preceded the major reinvigoration of convective deep-water formation in the Nordic Seas and abrupt Greenland warming; sea ice expansions preceded the buildup of a deep oceanic heat reservoir. Our findings suggest that the sea ice variability shaped regime shifts between surface stratification and deep convection in the Nordic Seas during abrupt climate changes

Sea ice variability in the southern Norwegian Sea during glacial Dansgaard-Oeschger climate cycles.

Ground was broken two weeks ago for the new women\u27s dormitory which will be known as Compton. Professor Robert Bonthius of the department of religion has resigned from the College of Wooster. He will be going to New York to be a chaplain and professor of religion at Vassar College. Five senior art majors will have their art on display beginning May 9th. Head of the department of chemistry, Dr. Roy I. Grady, will act in the place of Dean William Taeusch for the 1954-1955 school year.https://openworks.wooster.edu/voice1951-1960/1071/thumbnail.jp

Sea ice variability in the Nordic Seas over Dansgaard–Oeschger climate cycles during the last glacial – A biomarker approach

The Arctic sea ice cover is in fast transition. Resolving past sea ice fluctuations and its link with abrupt climate change might be key for a better understanding of yet unknown climatic consequences of future Arctic sea ice loss. The last glacial period was marked by recurring abrupt climate changes, referred to as Dansgaard–Oeschger (D–O) climate cycles. These D–O climate cycles and in particular the associated abrupt warming transitions by up to 15°C over Greenland happening within years or decades might have been linked to shifts in sea ice cover in the Nordic Seas. This PhD thesis aims at resolving and constraining the largely unknown millennialscale sea ice variability in the Nordic Seas and its pivotal role for abrupt climate changes during the D–O cycles based on empirical proxy data evidence. Novel sea ice reconstructions are mainly based on the sedimentary abundances of the sea ice algae biomarker IP25 and open-water phytoplankton biomarkers. This thesis includes two multi-decadal to centennial-scale biomarker sea ice records from the southern and central Norwegian Sea covering the time period ~30–40 thousand years ago, which reveal unprecedented insights into the nature of glacial sea ice fluctuations during D–O cycles (Papers 1 and 2). A comparison of these biomarker sea ice records with LOVECLIM model output data of sea ice cover (Paper 1) and a new bromine-enrichment sea ice record from the RECAP ice core (East Greenland) (Paper 2), sheds light on the mechanisms and timing of rapid sea ice shifts with respect to abrupt Greenland climate changes. A third biomarker sea ice record from the Eirik Drift south of Greenland elucidates the sea ice cover and export in the northwestern North Atlantic ~30–40 thousand years ago (Paper 3). This thesis also comprises a calibration based on a robust linear correlation between the sea ice index PIP25 in (sub-)Arctic surface sediments and modern spring sea ice concentration, which allows a quantification of past sea ice changes (Paper 2). The results presented in this thesis provide hitherto unknown details of spatiotemporal changes in glacial sea ice cover and tephra-assisted links to climate recorded in Greenland ice cores. Substantial rapid sea ice reductions and ocean overturning in the Norwegian Sea shaped the abrupt cold-to-warm D–O climate transitions, following a more gradual initial sea ice retreat. This reveals insights into sea ice-related feedbacks for abrupt D–O climate shifts and advances our understanding of abrupt transitions in the coupled ocean-sea ice-climate system during the last glacial

Stable isotope, UK'37, SST, chlorin, alkenone and TOC data of sediment cores GIK17927-2 and GIK17928-3

Upwelling intensity in the South China Sea has changed over glacial-interglacial cycles in response to orbital-scale changes in the East Asian Monsoon. Here, we evaluate new multi-proxy records of two sediment cores from the north-eastern South China Sea to uncover millennial-scale changes in winter monsoondriven upwelling over glacial Terminations I and II. On the basis of U/Th-based speleothem chronology, we compare these changes with sediment records of summer monsoondriven upwelling east of South Vietnam. Ocean upwelling is traced by reduced (UK'37-based) temperature and increased nutrient and productivity estimates of sea surface water (d13C on planktic foraminifera, accumulation rates of alkenones, chlorins, and total organic carbon). Accordingly, strong winter upwelling occurred north-west of Luzon (Philippines) during late Marine Isotope Stage 6.2, Heinrich (HS) and Greenland stadials (GS) HS-11, GS-26, GS-25, HS-1, and the Younger Dryas. During these stadials, summer upwelling decreased off South Vietnam and sea surface salinity reached a maximum suggesting a drop in monsoon rains, concurrent with speleothem records of aridity in China. In harmony with a stadial-to-interstadial see-saw pattern, winter upwelling off Luzon in turn was weak during interstadials, in particular those of glacial Terminations I and II, when summer upwelling culminated east of South Vietnam. Most likely, this upwelling terminated widespread deep-water stratification, coeval with the deglacial rise in atmospheric CO2. Yet, a synchronous maximum in precipitation fostered estuarine overturning circulation in the South China Sea, in particular as long as the Borneo Strait was closed when sea level dropped below -40 m