Abstract. Here, we establish a spatiotemporal evolution of the sea-surface
temperatures in the North Atlantic over Dansgaard–Oeschger (DO) events 5–8
(approximately 30–40 kyr) using the proxy surrogate reconstruction method. Proxy data
suggest a large variability in North Atlantic sea-surface temperatures during
the DO events of the last glacial period. However, proxy data availability is
limited and cannot provide a full spatial picture of the oceanic changes.
Therefore, we combine fully coupled, general circulation model simulations
with planktic foraminifera based sea-surface temperature reconstructions to
obtain a broader spatial picture of the ocean state during DO events 5–8. The
resulting spatial sea-surface temperature patterns agree over a number of
different general circulation models and simulations. We find that
sea-surface temperature variability over the DO events is characterized by
colder conditions in the subpolar North Atlantic during stadials than during
interstadials, and the variability is linked to changes in the Atlantic
Meridional Overturning circulation and in the sea-ice cover. Forced
simulations are needed to capture the strength of the temperature variability
and to reconstruct the variability in other climatic records not directly
linked to the sea-surface temperature reconstructions. This is the first time
the proxy surrogate reconstruction method has been applied to oceanic
variability during MIS3. Our results remain robust, even when age
uncertainties of proxy data, the number of available temperature
reconstructions, and different climate models are considered. However, we
also highlight shortcomings of the methodology that should be addressed in
future implementations.
Atmospheric CO2 concentrations (pCO2) varied on millennial timescales in phase with Antarctic temperature during the last glacial period. A prevailing view has been that carbon release and uptake by the Southern Ocean dominated this millennial‐scale variability in pCO2. Here, using Earth System Model experiments with an improved parameterization of ocean vertical mixing, we find a major role for terrestrial and oceanic carbon releases in driving the pCO2 trend. In our simulations, a change in Northern Hemisphere insolation weakens the Atlantic Meridional Overturning Circulation (AMOC) leading to increasing pCO2 and Antarctic temperatures. The simulated rise in pCO2 is caused in equal parts by increased CO2 outgassing from the global ocean due to a reduced biological activity and changed ventilation rates, and terrestrial carbon release as a response to southward migration of the Intertropical Convergence Zone. The simulated terrestrial release of carbon could explain stadial declines in organic carbon reservoirs observed in recent ice core δ13C measurements. Our results show that parallel variations in Antarctic temperature and pCO2 do not necessitate that the Southern Ocean dominates carbon exchange; instead, changes in carbon flux from the global ocean and land carbon reservoirs can explain the observed pCO2 (and δ13C) changes.
Abstract. Here we establish a spatio-temporal evolution of the sea-surface temperatures in the North Atlantic over Dansgaard Oeschger (DO) events 5-8 (c. 30-40 ka) using the proxy surrogate reconstruction method. Proxy data suggest a large variability in North Atlantic sea-surface temperatures during the DO-events of the last glacial period. However, proxy data availability is limited and cannot provide a full spatial picture of the oceanic changes. Therefore, we combine fully coupled, general circulation model simulations with planktic foraminifera based sea-surface temperature reconstructions to obtain a broader 5 spatial picture of the ocean state during DO-events 5-8. The resulting spatial sea-surface temperature patterns agree over a number of different general circulation models and simulations. We find that sea-surface temperature variability over the DOevents is characterized by colder conditions in the subpolar North Atlantic during stadials than during interstadials, and the variability is linked to changes in the Atlantic Meridional Overturning circulation, and in the sea-ice cover. Forced simulations are needed to capture the strength of the temperature variability and to reconstruct the variability in other climatic records not 10 directly linked to the sea-surface temperature reconstructions. Our results are robust to uncertainties in the age models of the proxy data, the number of available temperature reconstructions, and over a range of climate models.Copyright statement.
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