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.
Highlights
Antarctic ice cores document glacial-interglacial and millennial-scale variability in atmospheric pCO2 over the past 800 kyr
Because the speciation and isotopic composition of dissolved boron in seawater depends on seawater pH, and borate ion is the dominant species incorporated into planktic foraminiferal shells, their recorded d11B serves as a pH-proxy[17], and paleo-pH can be quantified if temperature and salinity can be constrained independently
Because N. pachyderma lives below the sea surface, this difference represents the difference between atmospheric pCO2 (‘air’) and the seawater pCO2 (‘pCO2cal’) at the calcification depth and growth season of N. pachyderma (DpCO2cal-air)
Summary
Antarctic ice cores document glacial-interglacial and millennial-scale variability in atmospheric pCO2 over the past 800 kyr. Regional reconstructions of past changes in surface ocean pCO2 and temperature are important for understanding how climate, ocean circulation and the carbon cycle are linked. Greenland and Antarctic ice core records document a millennial-scale bipolar seesaw in air temperature changes during late Pleistocene glaciations and deglaciations[3]. The last glacial period was characterized by millennialscale variability in atmospheric pCO2, with an increase of roughly 25 matm beginning during most of the Heinrich stadials, and peaking at or less than a thousand years after the onset of the interstadials[9]. This study aims to quantify the evolution of shallow subsurface ocean carbonate chemistry in the Norwegian Sea over the past 135 kyr, using the boron isotopic composition (d11B) recorded in fossil shells of the polar planktic foraminifer Neogloboquadrina pachyderma. To elucidate the causes of these variations in seawater carbonate chemistry, we compare our results with previously published reconstructions of temperature[14,15], sea-ice cover, input of terrestrial organic matter and primary productivity[16]
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