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Abstract: Water mass variations in the northeastern Atlantic Ocean along 20°W are analyzed with pentadal resolution over the past 15 years using data from four repeat occupations of a meridional hydrographic section running south from Iceland. The section was sampled in 1988, 1993, 1998, and 2003. The results are interpreted in the context of changes in air–sea forcing, ocean circulation, and water properties associated with the North Atlantic Oscillation (NAO). The NAO index oscillated around zero from 1984 to 1988, was strongly positive from 1989 to 1995, after which it shifted to lower positive, and occasionally negative values from 1996 to 2003. Previously published studies suggest that after the 1995–1996 shift of the NAO, the subpolar gyre largely retreated to the northwest in the northeastern Atlantic Ocean, resulting in an increasingly southeastern character of local water masses with time. Water property changes extending from the SubPolar Mode Water (SPMW) just below the seasonal pycnocline through the density range shared by Mediterranean Outflow Water and SubArctic Intermediate Water (SAIW) along 20°W are consistent with changes in wind-driven ocean circulation and air–sea heat flux associated with shifts in the NAO, especially after accounting for ocean memory. After periods of lower NAO index the SPMW is warmer, saltier, and lighter. At these same times, large increases of apparent oxygen utilization (AOU) and potential vorticity are found at the SPMW base, consistent with SPMW ventilation to lighter densities during lower NAO index periods. Deeper and denser in the water column, the cold, fresh, and dense SAIW signature within the permanent pycnocline that was most strongly present in 1993, near the culmination of a period of high NAO index, is much reduced in 1988 and 1998. In 2003, after a prolonged period of lower NAO index, increasing influence of warmer, saltier subtropical waters is clear within the permanent pycnocline. The deep penetration of the changes implies that they are caused primarily by circulation changes resulting from NAO-associated wind shifts, but changes in air–sea heat flux could also have played a role. [Copyright &y& Elsevier]

Abstract: In this paper, we review interdecadal climatic variability in the eastern tropical Pacific Ocean. This variability dominates the climatic fluctuations in the North Pacific on scales between ENSO and the centennial trend and is commonly referred to as the Pacific Decadal Oscillation or PDO. We include a historical overview and a summary of observational work that describes the surface, tropospheric and subsurface signatures of this variability. Descriptions of interdecadal variability are incomplete at best, mostly due to limitations in the observational record. We emphasize that the well-known “ENSO-like” sea surface temperature (SST) pattern describing the PDO may not be an accurate representation. In the eastern tropical Pacific, the SST maxima are displaced north and south of the equator with larger amplitudes in the northern branch near the coast of North America, which has significant implications for the troposphere-driven circulations. Several mechanisms have been proposed to explain the PDO. We review these mechanisms and models, which capture our present level of understanding of the problem. We conclude by reporting there is little evidence of both multidecadal variability and the centennial trend in the eastern tropical Pacific. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific. [Copyright &y& Elsevier]

• The area analysed is autotrophic over an annual cycle. • Marine net biological production is estimated at 19 mmol m−2 d−1 in O 2 equivalents. • Different dynamics can explain productivity peaks in different times of the year. • Water is oxygen undersaturated during the whole winter period. As part of the OSMOSIS project, a fleet of gliders surveyed the Porcupine Abyssal Plain site (Northeast Atlantic) from September 2012 to September 2013. Salinity, temperature, dissolved oxygen concentration and chlorophyll fluorescence were measured in the top 1000 m of the water column. Net community production (N) over an annual cycle using an oxygen-budget approach was compared to variations of several parameters (wind speed, mixing layer depth relative to euphotic depth, temperature, density, net heat flux) showing that the main theories (Critical Depth Hypothesis, Critical Turbulence Hypothesis, Heat-flux Hypothesis) can explain the switch between net heterotrophy to net autotrophy in different times of the year, The dynamics leading to an increase in productivity were related to shifts in regimes, such as the possible differences in nutrient concentration. The oxygen concentration profiles used for this study constitute a unique dataset spanning the entire productive season resulting in a data series longer than in previous studies. Net autotrophy was found at the site with a net production of (6.4 ± 1.9) mol m−2 in oxygen equivalents (or (4.3 ± 1.3) mol m−2 in carbon equivalents). The period exhibiting a deep chlorophyll maximum between 10 m and 40 m of depth contributed (1.5 ± 0.5) mol m−2 in oxygen equivalent to the total N. These results are greater than most previously published estimates. [ABSTRACT FROM AUTHOR]