Description: Highlights • Planktic foraminifera species show an Early Holocene 14C plateau analogous to the atmospheric 14C plateau at 10.2–9.6 cal ka. • Age-calibrated Early Holocene 14C plateau boundaries provide precise age control in 3 sediment cores on a 900 km long transect. • Differences between planktic foraminiferal and atmospheric 14C ages reveal the 14C reservoir age of local surface waters. • Different planktic species document different 14C reservoir ages characteristic of different surface and subsurface waters. To trace spatial variations in Holocene reservoir ages of surface and subsurface waters we studied narrowly spaced 14C records of planktic foraminifera in three high-sedimentation rate cores from the Nordic Seas, the Barents Sea continental margin and eastern Fram Strait. The two northern cores reveal a distinct Early Holocene 14C plateau in dates on the subsurface dweller Neogloboquadrina pachyderma at 9.3–9.1 14C ka. The plateau was tuned to an atmospheric 14C plateau at 9.0–8.7 14C ka that spans 10.2–9.6 calendar ka. These two plateau boundaries provide robust age control points to estimate short-term changes in sedimentation rate and to correlate paleoceanographic signals over 900 km along the West Spitsbergen Current. The difference between planktic and atmospheric 14C plateau ages suggests local 14C reservoir ages of 370–400 yr. Planktic foraminifera species that inhabit different water masses document different reservoir ages. By comparison, the subpolar N. incompta reveals a reservoir age of 150 yr, probably formed in well-mixed Atlantic-sourced waters during winter. The near-surface dweller Turborotalita quinqueloba shows an age of 290 yr in the Fram Strait, but one of 720 yr at the Barents Sea continental margin. The latter age suggests a calcification within old, meltwater-enriched Arctic surface waters admixed by the East Spitsbergen Current. Likewise, we assign an elevated reservoir age of 760 yr on mixed species at a Norwegian Sea site near 71°N to Preboreal meltwaters that spread from northern Norway far west, also documented by the spatial distribution of a coeval δ13C minimum of N. pachyderma.

Description: The last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric CO2 and 14C. We employed the “14C plateau-tuning technique” to a centennial-scale planktic 14C record of core MD08-3180 retrieved S.W. of the Azores Islands at ∼3060 m water depth to establish both a new standard of absolute age control and a record of past 14C reservoir ages of ocean surface waters. Both δ18O minima of G. bulloides and high planktic reservoir ages of ∼1600 to 2170 yr suggest two major melt water incursions that reached from the Labrador Sea up to the subtropics over Heinrich Stadial 1 (HS-1). In parallel, we established a record of (apparent) benthic ventilation ages that add the planktic 14C reservoir ages together with the benthic-planktic 14C age difference at the site and time of deposition, a sum finally adjusted to past changes in atmospheric 14C that occurred since the time of deep-water formation. Near the Azores apparent deep-water ages of the Last Glacial Maximum were as low as 340–740 yr, which suggests a lateral advection of young North Atlantic Deep Waters (NADW) from subpolar regions south of Iceland, in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep-water formation. During HS-1, local benthic ventilation ages increased up to 2200–2550 yr, thus suggest an incursion of old southern-source deep waters, an unstable regime that was interrupted by brief pulses of NADW incursion near 16, 15.6 cal. ka, and most salient, near 14.9/14.7 ka.

Description: 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.

Description: Modeling studies predict that changes in radiocarbon (14C) reservoir ages of surface waters during the last deglacial episode will reflect changes in both atmospheric 14C concentration and ocean circulation including the Atlantic Meridional Overturning Circulation. Tests of these models require the availability of accurate 14C reservoir ages in well-dated late Quaternary time series. We here test two models using plateau-tuned 14C time series in multiple well-placed sediment core age-depth sequences throughout the lower latitudes of the Atlantic Ocean. 14C age plateau tuning in glacial and deglacial sequences provides accurate calendar year ages that differ by as much as 500-2500 years from those based on assumed global reservoir ages around 400 years. This study demonstrates increases in local Atlantic surface reservoir ages of up to 1000 years during the Last Glacial Maximum, ages that reflect stronger trades off Benguela and summer winds off southern Brazil. By contrast, surface water reservoir ages remained close to zero in the Cariaco Basin in the southern Caribbean due to lagoon-style isolation and persistently strong atmospheric CO2 exchange. Later, during the early deglacial (16 ka) reservoir ages decreased to a minimum of 170-420 14C years throughout the South Atlantic, likely in response to the rapid rise in atmospheric pCO2 and Antarctic temperatures occurring then. Changes in magnitude and geographic distribution of 14C reservoir ages of peak glacial and deglacial surface waters deviate from the results of Franke et al. (2008) but are generally consistent with those of the more advanced ocean circulation model of Butzin et al. (2012).

Description: Oxygen and carbon stable isotope data for planktonic foraminifera species G. ruber white from core GIK13291-1 off NW Africa.