Mollusk shells from Peruvian archaeological middens provide brief (< 5 yr per shell) records of past marine conditions. Marine radiocarbon age, R, is recorded in shell carbonate at the time of precipitation. R varies with changes in upwelling: when radiocarbon-depleted sub-thermocline water wells up, R is large; increased contribution from radiocarbon-enriched surface water (due to seasonal cycles or an El Niño event) reduces R. Are molluscan records of R a useful proxy for Peruvian upwelling? If so, does R from archaeological shells reveal mid-Holocene upwelling changes that constrain the Holocene history of El Niño-Southern Oscillation (ENSO)? Profiles of R along ontogeny from early 20th century Argopecten purpuratus (bay scallop) shells and mid-Holocene A. purpuratus, Mesodesma donacium (surf clam), and Trachycardium procerum (cockle) shells from eight coastal Peru locations show that R varies by up to 530 ± 200 ¹⁴C yr within individual shells. El Niño events are easily detectable in post-1950s shell carbonate due to increased radiocarbon contrast between sub- and super-thermocline water from “bomb carbon,” but R differences between El Niño and La Niña shells from the early 20th century are subtle. Decreasing precision in older shells due to ¹⁴C decay makes detecting El Niño events in the archaeological past using radiocarbon very difficult. Because of intrashell radiocarbon variation, caution is prudent when using marine material for chronometry in variable upwelling environments. Based on modeling, mollusks that grow seasonally rather than year-round can skew long-term average (> 1 yr) R reconstructions by nearly 200 ¹⁴C yr toward R of the preferred growth season. Coldloving M. donacium, for example, records older marine reservoir ages on average than A. purpuratus in the same water, because A. purpuratus grows in both warm and cold conditions. Comparisons of R between species with opposite seasonal growth habits can compound this effect. Because of intrashell R variation, seasonal growth biases, and measurement uncertainties, a change in R due to past ENSO changes would have to be hundreds of ¹⁴C yr or greater to be identifiable. Thus far, clear evidence for such a Holocene change in R has not been seen.

The Arctic and North Atlantic underwent significant climactic changes since the Last Glacial Maximum (25,000 years before present (1950 AD); ka BP), but offsets in the timing of events between the two regions are poorly constrained due to age model uncertainties that arise from changing radiocarbon reservoir ages. Here, we use a relatively high-resolution, multi-proxy stable isotope and sedimentologic dataset from Eastern Fram Strait (ODP Leg 162 Site 986) marine sediments to constrain the timing of Svalbard/Barents Sea Ice Sheet decay and infer deglacial reservoir ages over the last 30 ka. We use magnetic susceptibility, inorganic and organic carbon, foraminiferal assemblage counts, planktonic foraminiferal isotopes, and iceberg-rafted debris proxies to infer glaciomarine and paleoclimactic processes in Eastern Fram Strait. Significant negative Neogloboquadrina pachyderma (sinistral) δ18O episodes from background levels at 18.8 ka (-3.0 /) and 20.4 ka (-0.8 /) (on a radiocarbon-based age model) are shown to indicate meltwater discharge events from the Svalbard/Barents Sea Ice Sheet during the early glacial termination (21-14.7 ka). To allow for direct comparison between the timing of Eastern Fram Strait meltwater events and North Atlantic climate changes, the ODP Site 986 age model is correlated to the well-dated Greenland Ice Sheet Project 2 (GISP2) ice core δ18O record. The refined age model suggests that 16.0 and 18.1 ka are more realistic estimates for the meltwater events, inferring surface ocean reservoir age shifts of 1750 ± 1050 years in Eastern Fram Strait during the early glacial termination. Trends in reservoir ages throughout the last deglaciation mirror Nordic Sea deep ocean circulation changes and previously reported trends in the sub-polar North Atlantic; however, reservoir ages appear to be greater in Eastern Fram Strait. We hypothesize that processes affecting the distribution of reservoir ages in the North Atlantic and Arctic (e.g. sea ice cover, meltwater input, and ocean circulation) may have resulted in larger reservoir ages in polar regimes than in sub-polar ones during the last deglaciation, analogous to contemporary distributions. In contrast to previous radiocarbon age model-based studies in the Nordic Seas that predict a significant meltwater event at ~19 ka, these findings show that rapid Svalbard/Barents Sea Ice Sheet decay began at 16 ka and suggest that uncertainty on the order of thousands of years may exist in previous paleoclimate studies with radiocarbon-based age models from the deglacial Nordic Seas and Arctic.

Afin d’étudier les changements hydrologiques passés du « lac Noir » (dernière phase lacustre de la mer Noire) et l’expression de la Dernière Déglaciation en Europe centrale, des techniques analytiques variées ont été mises en œuvre sur la carotte MD04-2790 : modélisation, développement de méthodes statistiques, géochimie élémentaire et isotopique. La reconstitution de l’évolution des âges réservoir du « lac Noir » au cours des 30 derniers millénaires a permis de mieux comprendre les réponses hydrologiques du bassin aux changements climatiques (variations du niveau du plan d’eau, phases de stratification, possible déstabilisation d’hydrates de gaz). L’âge de la dernière reconnexion du « lac Noir » avec la mer Méditerranée a été révisé à 9 000 ans BP. L’interprétation des isotopes du Nd en termes de provenance des sédiments a permis de mettre en évidence que les pulses d’eaux de fonte arrivant dans le « lac Noir » au cours de l’événement de Heinrich 1 provenaient de la désintégration de la calotte fennoscandinave. Un mécanisme régional d’interactions climatiques entre lacs proglaciaires et atmosphère a été proposé pour expliquer l’organisation temporelle particulière des pulses d’eaux de fonte. Nos résultats renforcent le paradigme de Denton qui suggère que des stades prolongés sont nécessaires au passage du mode climatique glaciaire au mode interglaciaire. / In order to study the past hydrologic changes of the Black Sea “Lake”, various analytical techniques were applied to study the core MD04-2790: modelling, development of statistical approaches, elemental and isotopic geochemistry. The reconstructed reservoir age changes of the Black Sea “Lake” were interpreted in terms of the hydrologic responses of the lake to glacial/deglacial climate changes (water level change, water column stratification, possible chlatrate dissociation). Calendar age of the Black Sea “Lake” last reconnection to global ocean was also revised to 9,000 yr BP. Finally, drastic changes in &#949;Nd values strongly suggest that sediments deposited in response to Deglacial Water Pulses (DWP) during Heinrich Event 1 (HE1) originated from the Fennoscandian Ice Sheet (FIS), providing the first direct evidence that the Black Sea “Lake” recorded the collapse of the FIS. The peculiar temporal organisation of DWPs suggests outbursts of proglacial lakes into Dniepr catchment as well as regional climatic interactions between proglacial lakes and atmosphere. The HE1-timing of the DWPs occurrence would indicate that FIS was involved in the N-Atlantic circulation reduction that shifted Earth climatic machine towards interglacial conditions in accordance with Denton’s paradigm.

Applications in paleontological research are far from being limited to taxonomic collection and identification. Nor is such research limited to working solely on fossil data. Actualistic paleontology is the study of modern or recent organisms and processes to better understand those of the past. The bulk of this body of research falls under the category of actualistic paleontology, and examines geochronological methods and error biases in dating biological specimens ranging in age from modern to thousands of years old. Although such methods are arguably not perfect, error rates of ± a few hundred to few thousand years can be extremely important when considering ecological relationships among both Holocene taxa and time-averaged paleocommunities, but quite diminished when considering implications on more traditional dating techniques for ancient strata. Regardless, understanding implications of time resolution is important in analyses of and comparisons between any biological dataset. The following chapters are united by quantitative and statistical management of data with varying levels of temporal resolution, and represent four manuscripts that either are in press or soon to be submitted for publication. / Ph. D.