Can the subtropical North Atlantic permanent thermocline be observed from space?

The analysis of remotely sensed altimeter data and in situ measurements shows that ERS 2 radar can monitor the ocean permanent thermocline from space. The remotely sensed sea level anomaly data account for similar to 2/3 of the temperature variance or vertical displacement of isotherms at a depth of similar to 550 m in the Subtropical North Atlantic Ocean near 32.5 degree N. This depth corresponds closely to the region of maximum temperature gradient in the permanent thermocline where near semi-annual internal vertical displacements reach 200 to 300 m. The gradient of the altimeter sea level anomaly data correlates well with measured ocean currents to a depth of 750 m. It is shown that observations from space can account for similar to 3/4 of the variance of ocean currents measured in situ in the permanent thermocline over a 2-y period. The magnification of the permanent thermocline displacement with respect to the displacement of the sea surface was determined as - x650 and gives a measure of the ratio of barotropic to baroclinic decay scale of geostrophic current with depth. The overall results are used to interpret an eight year altimeter data tie series in the Subtropical North Atlantic at 32.5 degree N which shows a dominant wave or eddy period near 200 days, rather than semi-annual and increases in energy propagating westward in 1995 (west of 25 degree W). The effects of rapid North Atlantic Oscillation climate change on ocean circulation are discussed. The altimeter data for the Atlantic were Fourier analysed. It is shown how the annual and semi-annual components relate to the seasonal maximum cholorophyll-a SeaWiFS signal in tropical and equatorial regions due to the lifting of the thermocline caused by seasonally varying ocean currents forced by wind stress.

Mediterranean marine copepods: basin-scale trends of the calanoid Centropages typicus

The Mediterranean Sea is located in a crossroad of mid-latitude and subtropical climatic modes that enhance contrasting environmental conditions over both latitudinal and longitudinal ranges. Here, we show that the large-scale environmental forcing is reflected in the basin scale trends of the adult population of the calanoid copepod Centropages typicus. The species is distributed over the whole Mediterranean basin, and maximal abundances were found in the north-western basin associated to oceanic fronts, and in the Adriatic Sea associated to shallow and semi enclosed waters. The peak of main abundances of C. typicus correlates with the latitudinal temperature gradient and the highest seasonal abundances occurred in spring within the 14–18°C temperature window. Such thermal cline may define the latitudinal geographic region where C. typicus seasonally dominates the >200 μm-sized spring copepod community in the Mediterranean Sea. The approach used here is generally applicable to investigate the large-scale spatial patterns of other planktonic organisms and to identify favourable environmental windows for population development.