Modulation of sea surface temperature warming in the Bay of Biscay by Loire and Gironde Rivers

The influence of Loire and Gironde River discharges over the sea surface temperature (SST) in the eastern Bay of Biscay (0.6º–36.6ºW, 44.2º–47.8ºW) was analyzed by means of two complementary databases (MODIS and OISST1/4). The area influenced by river plume showed a different SST when compared with the adjacent oceanic area for the months when the plume attains its highest extension (December, January, and February). Ocean was observed to warm at a rate of approximately 0.3ºC dec−1 while temperature at the area influenced by the rivers cooled at a rate of −0.15ºC dec−1 over the period 1982–2014. The mere presence of a freshwater layer is able to modulate the warming observed at adjacent ocean locations since the coastal area is isolated from the rest of the Bay. This nearshore strip is the only part of the Bay where changes in SST depend on North Atlantic Oscillation (NAO) but not on North Atlantic SST represented by the Atlantic Multidecadal Oscillation (AMO). These different cooling-warming trends are even more patent over the last years (2002–2014) under atmospheric favorable conditions for plume enhancement. River runoff increased at a rate on the order of 120 m3s−1dec−1 over that period and southwesterly winds, which favor the confinement of the plume, showed a positive and significant trend both in duration and intensity. Thus, the coastal strip has been observed to cool at a rate of −0.5°C dec−1.

Interglacials of the last 800,000 years

Interglacials, including the present (Holocene) period, are warm, low land ice extent (high sea level), end-members of glacial cycles. Based on a sea level definition, we identify eleven interglacials in the last 800,000years, a result that is robust to alternative definitions. Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (last interglacial) and 11c (similar to 400ka ago) were globally strong (warm), while MIS 13a (similar to 500ka ago) was cool at many locations. A step change in strength of interglacials at 450ka is apparent only in atmospheric CO2 and in Antarctic and deep ocean temperature. The onset of an interglacial (glacial termination) seems to require a reducing precession parameter (increasing Northern Hemisphere summer insolation), but this condition alone is insufficient. Terminations involve rapid, nonlinear, reactions of ice volume, CO2, and temperature to external astronomical forcing. The precise timing of events may be modulated by millennial-scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere. A variety of temporal trends is observed, such that maxima in the main records are observed either early or late in different interglacials. The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes. Interglacials have been typically 10-30ka long. The combination of minimal reduction in northern summer insolation over the next few orbital cycles, owing to low eccentricity, and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future.