Episodic release of CO2 from the high-latitude North Atlantic Ocean during the last 135 kyr

Abstract

Antarctic ice cores document glacial-interglacial and millennial-scale variability in atmospheric pCO2 over the past 800 kyr. The ocean, as the largest active carbon reservoir on this timescale, is thought to have played a dominant role in these pCO2 fluctuations, but it remains unclear how and where in the ocean CO2 was stored during glaciations and released during (de)glacial millennial-scale climate events. The evolution of surface ocean pCO2 in key locations can therefore provide important clues for understanding the ocean's role in Pleistocene carbon cycling. Here we present a 135-kyr record of shallow subsurface pCO2 and nutrient levels from the Norwegian Sea, an area of intense CO2 uptake from the atmosphere today. Our results suggest that the Norwegian Sea probably acted as a CO2 source towards the end of Heinrich stadials HS1, HS4 and HS11, and may have contributed to the increase in atmospheric pCO2 at these times.

Atmosphere‐Ocean CO2 Exchange Across the Last Deglaciation From the Boron Isotope Proxy

“…At sites where the carbonate system is strongly affected by seasonality and the fluxes of planktic foraminiferal tests have distinct seasonal patterns, the pH and thus pCO 2 estimates will likely be biased toward the season of maximum production. Also, since foraminifers calcify over a range of depths instead of strictly at the surface, the composite may be biased toward higher pCO 2 because seawater pCO 2 increases with depth within the top few hundreds of meters (Ezat et al, ; Raitzsch et al, ; Taylor et al, ; Yu et al, ). However, we found that these complexities would only have minor effects on our composite pCO 2 (Figures S6 and S7), probably because the calibrations that are largely based on core top measurements that already account for some of these effects.…”

“…The calibration used for Neogloboquadrina pachyderma ( N. pachyderma ) is δ 11 B borate = δ 11 B CaCO3 +3.38 ± 0.72‰ (first calibrated by Yu et al, , later confirmed by Gray, Weldeab, et al, over a wider range of pH). For the N. pachyderma JM11 record generated by NTIMS (Ezat et al, ), we used the original intercept of 2.053‰ (Ezat et al, , NTIMS) instead of 3.38‰ (Gray, Weldeab, et al, , MC‐ICP‐MS) to account for technique/machine offsets. Applying the T. sacculifer calibration curve to the Holocene δ 11 B of NIOP464 (Palmer et al, , NTIMS) and EDRC92 (Palmer & Pearson, , NTIMS) resulted in very different pH from the original publication, due to technique/machine offsets.…”

“…By taking advantage of the calibrated boron‐pH proxy, a number of studies have investigated the history of ocean‐atmosphere CO 2 exchange across the last deglaciation from sites in the tropical Pacific (Martínez‐Botí et al, ; Palmer & Pearson, ), the North Pacific (Gray, Rae, et al, ), the North Indian Ocean (Naik et al, ; Palmer et al, ), the tropical Atlantic (Foster, ; Foster & Sexton, ; Henehan et al, ), the North Atlantic (Ezat et al, ; Yu et al, ), and the South Atlantic (Martínez‐Botí et al, ; Figure a). Collectively, the available records reveal millennial‐scale δ 11 B variations that reflect substantial changes in air‐sea ∆pCO 2 over the deglaciation (Figure ).…”

“…(a) δ 11 B measured in Trilobatus sacculifer , ODP1238 (red; Martínez‐Botí et al, ), EDRC92 (brown; Palmer & Pearson, ) and NIOP464 (pink; Palmer et al, ). (b) δ 11 B measured in Neogloboquadrina pachyderma , RAPiD‐15‐4p (yellow; Yu et al, ), MD01‐2416 (blue; Gray, Weldeab, et al, ) and JM11‐PI‐19PC (dark purple; Ezat et al, ). (c) δ 11 B measured in Globigerinoides ruber , GeoB1105 (orange; Foster & Sexton, ), ODP999 (light purple; Foster, ), GeoB1523 (dark green; Henehan et al, ) and AAS9 (gray; Naik et al, ).…”

Two‐Timescale Carbon Cycle Response to an AMOC Collapse

“…The present results find that after one millennium, in addition to the fast terrestrial release of carbon, the ocean accounts for an equal but more gradual release of CO 2 due to a combination of reduced biological activity, particularly in the Atlantic, and deep ocean ventilation in the Pacific sector of the Southern Ocean. While there is evidence of increased Southern Ocean upwelling during stadials (Anderson et al, ), recent ocean sediment δ 11 B results from the Nordic Seas support the possible release of carbon in the North Atlantic (Ezat et al, ).…”