ALBERT

Description: Highlights • North Atlantic records indicate an intense Heinrich stadial (HS) during Termination V. • The HS probably resulted from extreme glacial conditions during MIS12. • The HS curtailed AMOC, shaping TV via meridional heat transport anomalies. • The rate of CO2 release during the HS of TV was lower than during HS1. • North Atlantic overturning during MIS11 was enhanced with respect to the Holocene. Abstract The role of millennial scale climate variability in supplementing the astronomical forcing of glacial–interglacial transitions remains a major unresolved question. Here we compare the occurrence and character of “terminal” ice rafting events in both the North and South Atlantic during the last deglaciation (Termination I, TI) and during the transition between Marine Isotope Stages (MIS) 12 and 11 (or Termination V, TV). We show that TV experienced a massive terminal ice rafting event in the North Atlantic that was more intense and longer lasting than Heinrich event 1 (H1) of the last deglaciation. This massive ice rafting event was linked to cold stadial conditions and reduced deep water formation in the North Atlantic, in parallel with warming at high southern latitudes, similar to the bipolar seesaw pattern exhibited during H1 over the last deglaciation. We propose that the particular intensity and duration of the TV ice rafting event resulted from the especially large volume of Northern Hemisphere ice sheets during MIS12. In turn, the unusually long duration and large amplitude of TV likely resulted from the exceptionally prolonged collapse of the AMOC during the TV Heinrich stadial, and from a subsequent transient AMOC “overshoot” with respect to later MIS11 interglacial circulation. Furthermore, we suggest that the intense Heinrich stadial of TV contributed to the deglaciation primarily via meridional heat transport anomalies that would have enhanced the incipient warming arising from relatively weak insolation forcing, and only secondarily via CO2 release.

Description: The role of millennial scale climate variability in supplementing the astronomical forcing of glacial-interglacial transitions remains a major unresolved question. Here we compare the occurrence and character of "terminal" ice rafting events in both the North and South Atlantic during the last deglaciation (Termination I, TI) and during the transition between Marine Isotope Stages (MIS) 12 and 11 (or Termination V. TV). We show that TV experienced a massive terminal ice rafting event in the North Atlantic that was more intense and longer lasting than Heinrich event 1 (H1) of the last deglaciation. This massive ice rafting event was linked to cold stadial conditions and reduced deep water formation in the North Atlantic, in parallel with warming at high southern latitudes, similar to the bipolar seesaw pattern exhibited during H1 over the last deglaciation. We propose that the particular intensity and duration of the TV ice rafting event resulted from the especially large volume of Northern Hemisphere ice sheets during MIS12. In turn, the unusually long duration and large amplitude of TV likely resulted from the exceptionally prolonged collapse of the AMOC during the TV Heinrich stadia], and from a subsequent transient AMOC "overshoot" with respect to later MIS11 interglacial circulation. Furthermore, we suggest that the intense Heinrich stadial of TV contributed to the deglaciation primarily via meridional heat transport anomalies that would have enhanced the incipient warming arising from relatively weak insolation forcing, and only secondarily via CO2 release

Description: Accurate reconstruction of past ocean temperatures is of critical importance to paleoclimatology. Carbonate clumped isotope thermometry ("L'l47") is a relatively recent technique based on the strong relationship between calcification temperature and the statistical excess of 13C- 180 bonds in carbonates. Its application to foraminifera holds great scientific potential, particularly because Ll47 paleotemperature reconstructions do not require assumptions regarding the 180 composition of seawater. However there are still relatively few published observations investigating the potential influence of parameters such as salinity or foraminiferal size and species. We present a new calibration data set based on 234 replicate analyses of9 planktonic and 2 benthic species of foraminifera collected from recent core-top sediments, with calcification temperatures ranging from -2 to 25 °C. We observe a strong relationship between Ll47 values and independent, oxygen-IS estimates of calcification temperatures: L'l47 = 41.63 x 103 /T2 + 0.2056 The formal precision of this regression(± 0.7-1.0 °C at 95 % confidence level) is much smaller than typical analytical errors. Our observations confirm the absence of significant species-specific biases or salinity effects. We also investigate potential foraminifer size effects between 200 and 〉560 μm in 6 species, and conclude that all size fractions from a given core-top location and species display statistically undistinguishable L'l47 values. These findings provide a robust foundation for future interlaboratories comparisons and paleoceanographic applications.