North Atlantic subpolar gyre along predetermined ship tracks since 1993: a monthly data set of surface temperature, salinity, and density

We present a binned product of sea surface temperature, sea surface salinity, and sea surface density data in the North Atlantic subpolar gyre from 1993 to 2017 that resolves seasonal variability along specific ship routes (https://doi.org/10.6096/SSS-BIN-NASG). The characteristics of this product are described and validated through comparisons to other monthly products. Data presented in this work were collected in regions crossed by two predetermined ship transects, between Denmark and western Greenland (AX01) and between Iceland, Newfoundland, and the northeastern USA (AX02). The data were binned along a selected usable transect. The analysis and the strong correlation between successive seasons indicate that in large parts of the subpolar gyre, the binning approach is robust and resolves the seasonal timescales, in particular after 1997 and in regions away from the continental shelf. Prior to 2002, there was no winter sampling over the West Greenland Shelf. Variability in sea surface salinity increases towards Newfoundland south of 54°&thinsp;N, as well as in the western Iceland Basin along 59°&thinsp;N. Variability in sea surface temperature presents less spatial structure with an increase westward and towards Newfoundland. The contribution of temperature variability to density dominates in the eastern part of the gyre, whereas the contribution of salinity variability dominates in the southwestern part along AX02.</p

Climate-driven range extension of Amphistegina (protista, foraminiferida) : models of current and predicted future ranges

© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS ONE 8 (2013): e54443, doi:10.1371/journal.pone.0054443.Species-range expansions are a predicted and realized consequence of global climate change. Climate warming and the poleward widening of the tropical belt have induced range shifts in a variety of marine and terrestrial species. Range expansions may have broad implications on native biota and ecosystem functioning as shifting species may perturb recipient communities. Larger symbiont-bearing foraminifera constitute ubiquitous and prominent components of shallow water ecosystems, and range shifts of these important protists are likely to trigger changes in ecosystem functioning. We have used historical and newly acquired occurrence records to compute current range shifts of Amphistegina spp., a larger symbiont-bearing foraminifera, along the eastern coastline of Africa and compare them to analogous range shifts currently observed in the Mediterranean Sea. The study provides new evidence that amphisteginid foraminifera are rapidly progressing southwestward, closely approaching Port Edward (South Africa) at 31°S. To project future species distributions, we applied a species distribution model (SDM) based on ecological niche constraints of current distribution ranges. Our model indicates that further warming is likely to cause a continued range extension, and predicts dispersal along nearly the entire southeastern coast of Africa. The average rates of amphisteginid range shift were computed between 8 and 2.7 km year−1, and are projected to lead to a total southward range expansion of 267 km, or 2.4° latitude, in the year 2100. Our results corroborate findings from the fossil record that some larger symbiont-bearing foraminifera cope well with rising water temperatures and are beneficiaries of global climate change.This work was supported by grants from the German Science Foundation (DFG; www.dfg.de) to ML and SL (LA 884/10-1, LA 884/5-1)

Middle-late Pleistocene deep water circulation in the southwest subtropical Pacific

International audienceThe modern δ13CDIC distribution in southwest subtropical Pacific deep waters is consistent with a regional mixing regime between water masses of open Pacific Ocean and Tasman Sea origin. This mixing regime is reconstructed across the middle-late Pleistocene using a record of benthic foraminiferal δ13C in a sediment core from the New Caledonia Trough. The relative influence on the mixing regime from open Pacific Ocean deep waters is seen to be significantly reduced during glacial in comparison to interglacial stages over the past 1.1 Ma. The spatial δ13C gradient in the Southern Ocean between deep waters entering the Tasman Sea and the open Pacific Ocean is shown to be consequently greater during glacial than interglacial stages but was generally reduced across the period of the Middle Pleistocene Transition. The existence of strong spatial chemical gradients in the glacial Southern Ocean limits its capacity to act as an enhanced sink for atmospheric carbon

Warming of the Upper Equatorial Indian Ocean and Changes in the Heat Budget (1960-99)

International audienceIn the equatorial Indian Ocean, sea surface has warmed by 0.5°-1°C over the 1960-99 period, while waters have cooled at thermocline depth and the net atmospheric heat flux has decreased. Among a set of twentieth-century climate simulations from 12 coupled models, the Centre National de Recherches Météorologiques Coupled Global Climate Model version 3 (CNRM-CM3) reproduces key observed features of these changes. It is used to investigate changes in the heat budget of the upper equatorial Indian Ocean and identify mechanisms responsible for the warming. By comparing twentieth-century and control simulations, significant shifts in the mean balance of the heat budget between the preindustrial and the 1960-99 periods can be identified. The main cause of the surface warming is a decrease in the upwelling-related oceanic cooling. It occurs in the thermocline dome region because of a slowdown of the wind-driven Ekman pumping. The observed decrease in net heat flux is a negative feedback driven by evaporation, which is enhanced by the equatorial warming and associated strengthening of trade winds

Climatic variability in the vicinity of Wallis, Futuna, and Samoa islands (13 degrees-15 degrees S, 180 degrees-170 degrees W)

h-lean conditions, seasonal, and ENSO-related (El Nine Southern Oscillation) variability in the vicinity of Wallis, Futuna, and Samoa islands (13 degrees-15 degrees S, 180 degrees-170 degrees W) over the 1973-1995 period are analysed for wind pseudostress, satellite-derived and in situ precipitation, sea surface temperature (SST) and salinity (SSS), sea level, and 0-450 m temperature and geostrophic current. The mean local conditions reflect the presence of the large scale features such as the western Pacific warm pool, the South Pacific Convergence Zone (SPCZ), and the South Pacific anticyclonic gyre. The seasonal changes are closely related to the meridional migrations of the SPCZ, which passes twice a year over the region of study. During the warm phase of ENSO (El Nino), we generally observe saltier-than-average SSS (of the order of 0.4), consistent with a rainfall deficit (0.4 m yr(-1)), a hint of colder-than-average surface temperature is also identified in subsurface (0.3 degrees C), a weak tendency for westward geostrophic current anomalies (2 cm s(-1) at the surface), a sea level decrease (5-10 cm), together with easterly (5 m(2) s(-2)) and well marked southerly (10 m(2) s(-2)) wind pseudo-stress anomalies. Anomalies of similar magnitude, but of opposite sign, are detected during the cold phase of ENSO (La Nina). While these ENSO-related changes apply prior to the 1990s, they were nor observed during the 1991-1994 period, which appears atypical.Les conditions climatiques moyennes, les variations saisonnières et interannuelles associées au phénomène El Niño Oscillation Australe (ENOA) de la région située au voisinage des îles Wallis, Futuna et Samoa (13°–15°S, 180°–170° W) sont décrites pour les années 1973–1995. Les paramètres analysés comprennent la pseudo-tension du vent, les précipitations (estimations satellitales et mesures in situ), la température et la salinité de surface, le niveau de la mer, les profils verticaux 0–450 m de température et de courant géostrophique. Pour l'ensemble des paramètres, les conditions moyennes traduisent la présence des structures à grandes échelles du Pacifique tropical, à savoir les eaux chaudes (>28 °C) du Pacifique ouest, la zone de convergence des vents et le grand tourbillon anticyclonique du Pacifique sud. Les variations saisonnières sont pour l'essentiel liées à la migration nord-sud de la zone de convergence du Pacifique sud qui passe deux fois par an sur la région d'étude. Au cours de la phase chaude du phénomène ENOA (El Niño), on observe en général une salinité supérieure à la normale (de l'ordre de 0,4), cohérente avec une baisse des précipitations (−0,4 m an−1), une tendance au refroidissement des eaux de surface et de subsurface (−0,3 °C), une anomalie de courant géostrophique dirigée vers l'ouest (−2 cm s−1 à la surface), une baisse du niveau de la mer (−5 à −10 cm), ainsi qu'une diminution modérée de la composante est-ouest des alizés (−5 m2s−2) et un renforcement marqué de la composante sud-nord (+10 m2s−2). Les anomalies observées au cours de la phase chaude d'ENOA (El Niño) sont du même ordre de grandeur mais de signe opposé au cours de la phase froide d'ENOA (La Niña). Ces anomalies s'appliquent à la période antérieure à 1990, mais non à la période 1991–1994 qui apparaît comme «inhabituelle

Observed temperature trends in the Indian Ocean over 1960-1999 and associated mechanisms

The linear trends in oceanic temperature from 1960 to 1999 are estimated using the new Indian Ocean Thermal Archive (IOTA), a compilation of historical temperature profiles. Widespread surface warming is found, as in other data sets, and reproduced in IPCC climate model simulations for the 20th century. This warming is particularly large in the subtropics, and extends down to 800 m around 40–50°S. Models suggest the deep-reaching subtropical warming is related to a 0.5° southward shift of the subtropical gyre driven by a strengthening of the westerly winds, and associated with an upward trend in the Southern Annular Mode index. In the tropics, IOTA shows a subsurface cooling corresponding to a shoaling of the thermocline and increasing vertical stratification. Most models suggest this trend in the tropical Indian thermocline is likely associated with the observed weakening of the Pacific trade winds and transmitted to the Indian Ocean by the Indonesian throughflow