Overview of the various models for ice ages in the recent past (3 MYBP to present) - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 219

different. This heat flux will result in changes in weather patterns and climatic
conditions.
The consensus view of the role of the oceans in controlling and contributing
to climate change was discussed at length by Rahmstorf (2002). As a result of
their heat capacity and circulation, the oceans store and redistribute large
amounts of heat before releasing it to the atmosphere (via latent heat in the form
of water vapor) or radiating it back into space. The northern North Atlantic, the
Ross Sea, and the Weddell Sea were identified as key areas for the thermohaline
circulation of the world oceans in which surface waters reach a critical density and
sink after releasing heat to the atmosphere.
In addition to their heat storage and transport effects, the oceans influence the
Earth's heat budget through sea ice cover, which alters planetary albedo. Sea ice
also acts as an effective thermal blanket, insulating the ocean from the overlying
atmosphere. According to Rahmstorf (2002):
''This is so effective that in a typical ice-covered sea more than half of the
air-sea heat exchange occurs through patches of open water (leads) that make up
around 10% of the surface area.''
The oceans also affect the climate system by participating in biogeochemical
cycles and exchanging gases with the atmosphere, thus influencing its greenhouse
gas content:
''The oceans contain about fifty times more carbon than the atmosphere, and
theories seeking to explain the lower concentrations of atmospheric carbon
dioxide that prevailed during glacial times invariably invoke changes in the
oceanic carbon sink, either through physical or biological mechanisms (the
so-called 'biological pump').''
Rahmstorf (2002) focused on the role of ocean circulation changes in major
climate changes during the past 120,000 years, since the Eemian interglacial.
However, he perhaps over-modestly cautioned that ''controversies remain over
many issues, and the interpretation I have attempted here is subjective and will
probably turn out to be partly wrong.''
Rahmstorf (2002) described ocean circulation (see Figure 8. 3 ). He suggested
that three distinct circulation modes prevailed in the Atlantic Ocean at different
times, depending on the mode of formation of North Atlantic Deep Water
(NADW). These are labeled as the interstadial (warm), stadial (cold), and
Heinrich (off) modes. They are illustrated schematically i n Figure 8. 4 . In the inter-
stadial mode, near-surface ocean currents persist up to higher latitudes and, as
they cool and their salinity increases, NADW is formed in the Nordic seas and
drops to great depths for return to the south. In the stadial mode, NADW is
formed in the subpolar open North Atlantic (i.e., south of Iceland) and does not
achieve the density of the interstadial mode, so the return flow is not as deep. In
the Heinrich mode, NADW formation all but ceases and waters of Antarctic