Long-term Variability Of Sea Surface Temperature Research Articles

Long-term variability of the western tropical Atlantic sea surface temperature driven by greenhouse gases and AMOC

The long-term orbital-scale sea surface temperature (SST) variability in the tropics is thought to be mainly driven by greenhouse gases (GHG) forcing. However, few studies have investigated the drivers of such variability in the tropical Atlantic. Given the evidence of orbital-scale changes in Atlantic Meridional Overturning Circulation (AMOC) strength, one can hypothesize that AMOC variability also modulates the long-term tropical Atlantic SST through the bipolar seesaw mechanism. According to this mechanism, under weak [strong] AMOC conditions, the Southern Hemisphere is expected to warm up [cool down], while the Northern Hemisphere cools down [warms up]. Here, we investigate the long-term SST variability of the western tropical South Atlantic (WTSA), i.e., along the main pathway of the upper AMOC branch towards the equator, using a new 300 thousand years (kyr)-long Mg/Ca-based SST record. Our SST record shows glacial-interglacial variability superimposed by four remarkable long-term warm events during the three recorded glacial periods. These glacial warm events occurred between ca. 280–260, 160–143, 75–60, and 40–24 ka before present. Our results support the notion that atmospheric GHG plays a leading role in modulating the glacial-interglacial SST variability in the WTSA. However, it does not explain the occurrence of glacial warm events. Our study supports that the glacial warm events were caused by an orbital-scale bipolar seesaw mechanism operating in the Atlantic due to changes in the AMOC strength. These warm events may have been amplified by annual mean insolation driven by obliquity. Finally, we suggest that the long-term bipolar seesaw warmed the western tropical (South) Atlantic during the MIS 5/4 transition when the Earth's climate was cooling off.

Interannual variability of sea surface temperature at the polar latitudes of the Atlantic Ocean

The general regularities and regional differences in the interannual variability of the sea surface temperature in the polar latitudes of the Atlantic Ocean are revealed according to the OI SST reanalysis data for period 1982—2017. The reanalysis contains daily average sea surface temperature values at the nodes of a regular grid 0,25°×0,25°. In this work, areas where the ice concentration did not exceed
 90 % were analyzed. In both polar basins, the position of areas with a high level of sea surface temperature
 interannual variability qualitatively coincides with the position of intense currents. The maximum values of
 linear sea surface temperature trends are observed in areas of the maximum level of interannual variability,
 while the trends in long-term sea surface temperature variability in the Arctic and Antarctic are noticeably
 different. Significant positive sea surface temperature trends prevail in the Atlantic sector of the Arctic.
 Significant negative trends have been identified only off the northeastern coast of Greenland and north of the Arctic Current. The sea surface temperature decrease on a long-term scale in this area is associated with an increase of cold water transport by the East Greenland and Arctic currents, which are formed as a result
 of the intensive melting of Arctic ice observed in recent decades. In the Atlantic sector of the Antarctic, on the contrary, significant negative sea surface temperature trends prevail. In the Arctic, the maximum values of positive sea surface temperature trends are observed in August—September during the period of maximum warming of surface waters and minimum concentration of drifting ice. In the Antarctic, the maximum negative sea surface temperature trends in absolute value are observed from August to October, during the period of surface water cooling and maximum ice concentration.

Regime shift of the South China Sea SST in the late 1990s

Decadal variability of the South China Sea (SCS) sea surface temperature (SST) during 1982–2014 is investigated using observations and ocean reanalysis datasets. The SCS SST shows an abrupt transition from a cold-to-warm regime in the late 1990s. Based on the long-term SST variability two epochs are defined, 1982–1996 and 2000–2014 as cold and warm regimes respectively, spanning on either side of the 1997–1999 SCS warming. Despite the occurrence of strong El Nino induced warming events, the SST anomalies tend to be negative in the cold regime. Conversely during the warm regime, the positive SST anomalies have dominated over the La Nina driven cooling events. The cold (warm) SST regime is marked by net heat gain (loss) by the SCS. The long-term variations of net surface heat flux are mainly driven by the latent heat flux anomalies while the short wave flux plays a secondary role. Low-frequency variability of the South China Sea throughflow (SCSTF) appears to be closely related to the SCS SST regime shift. The SCSTF shows reversing trends during the cold and warm epochs. The weakened SCSTF in the warm regime has promoted the SCS warming by limiting the outward flow of warm water from the SCS. Meanwhile, enhanced SCSTF during the cold regime acts as a cooling mechanism and lead to persistent negative SST anomalies. The change in trend of the SCSTF and SST regime shift coincides with the switching of pacific decadal oscillation from a warm to cold phase in the late 1990s.

The long-term variability of sea surface temperature in the seas east of China in the past 40 a

The global surface temperature change since the mid-19th century has caused general concern and intensive study. However, long-term changes in the marginal seas, including the seas east of China, are not well understood because long-term observations are sparse and, even when they exist, they are over limited areas. Preliminary results on the long-term variability of sea surface temperature (SST) in summer and winter in the seas east of China during the period of 1957-2001 are reported using the Ocean Science Database of Institute of Oceanology, Chinese Academy of Sciences, the coastal hydrological station in situ and satellite data. The results show well-defined warming trends in the study area. However warming and cooling trends vary from decade to decade, with steady and rapid warming trends after the 1980s and complicated spatial patterns. The distribution of SST variation is intricate and more blurred in the areas far away from the Kuroshio system. Both historical and satellite data sets show significant warming trends after 1985. The warming trends are larger and spread to wider areas in winter than in summer, which means decrease in the seasonal cycle of SST probably linked with recently observed increase of the tropical zooplanlcton species in the region. Spatial structures of the SST trends are roughly consistent with the circulation pattern especially in winter when the meridional SST gradients are larger, suggesting that a horizontal advection may play an important role in the long-term SST variability in winter.

Long-term sea surface temperature variability in the Aegean Sea

The inter-annual/decadal scale variability of the Aegean Sea Surface Temperature (SST) is investigated by means of long-term series of satellite-derived and in situ data. Monthly mean declouded SST maps are constructed over the 1985–2008 period, based on a re-analysis of AVHRR Oceans Pathfinder optimally interpolated data over the Aegean Sea. Basin-average SST time series are also constructed using the ICOADS in situ data over 1950–2006. Results indicate a small SST decreasing trend until the early nineties, and then a rapid surface warming consistent with the acceleration of the SST rise observed on the global ocean scale. Decadal-scale SST anomalies were found to be negatively correlated with the winter North Atlantic Oscillation (NAO) index over the last 60 years suggesting that along with global warming effects on the regional scale, a part of the long-term SST variability in the Aegean Sea is driven by large scale atmospheric natural variability patterns. In particular, the acceleration of surface warming in the Aegean Sea began nearly simultaneously with the NAO index abrupt shift in the mid-nineties from strongly positive values to weakly positive/negative values.

Long-term sea surface temperature variability in the Aegean Sea

The inter-annual/decadal scale variability of the Aegean Sea Surface Temperature (SST) is investigated by means of long-term series of satellite-derived and in situ data. Monthly mean declouded SST maps are constructed over the 1985–2008 period, based on a re-analysis of AVHRR Oceans Pathfinder optimally interpolated data over the Aegean Sea. Basin-average SST time series are also constructed using the ICOADS in situ data over 1950–2006. Results indicate a small SST decreasing trend until the early nineties, and then a rapid surface warming consistent with the acceleration of the SST rise observed on the global ocean scale. Decadal-scale SST anomalies were found to be negatively correlated with the winter North Atlantic Oscillation (NAO) index over the last 60 years suggesting that along with global warming effects on the regional scale, a part of the long-term SST variability in the Aegean Sea is driven by large scale atmospheric natural variability patterns. In particular, the acceleration of surface warming in the Aegean Sea began nearly simultaneously with the NAO index abrupt shift in the mid-nineties from strongly positive values to weakly positive/negative values.

Long-Term Sea Surface Temperature Variability along the U.S. East Coast

Abstract Sea surface temperature variations along the entire U.S. East Coast from 1875 to 2007 are characterized using a collection of historical observations from lighthouses and lightships combined with recent buoy and shore-based measurements. Long-term coastal temperature trends are warming in the Gulf of Maine [1.0° ± 0.3°C (100 yr)−1] and Middle Atlantic Bight [0.7° ± 0.3°C (100 yr)−1], whereas trends are weakly cooling or not significant in the South Atlantic Bight [−0.1° ± 0.3°C (100 yr)−1] and off Florida [−0.3° ± 0.2°C (100 yr)−1]. Over the last century, temperatures along the northeastern U.S. coast have warmed at a rate 1.8–2.5 times the regional atmospheric temperature trend but are comparable to warming rates for the Arctic and Labrador, the source of coastal ocean waters north of Cape Hatteras (36°N). South of Cape Hatteras, coastal ocean temperature trends match the regional atmospheric temperature trend. The observations and a simple model show that along-shelf transport, associated with the mean coastal current system running from Labrador to Cape Hatteras, is the mechanism controlling long-term temperature changes for this region and not the local air–sea exchange of heat.

Long-term variability of surface temperature in the Black Sea, and its connection with the large-scale atmospheric forcing

Satellite, in situ and reanalysis data for the period of 1950–2005 were used to study the long-term variability of sea surface temperature (SST) in the Black Sea and its connection with the major large-scale atmospheric forcing (air temperature, surface wind and North Atlantic Oscillation — NAO). In contrast to the quasi-regular decadal oscillations of the SST typical for the Northern Atlantic, the pattern of long-term SST variability in the Black Sea is better described as an intermittent periods of SST increase/decrees with the duration of approximately 6–10 years and short (1–2 years) and quite abrupt transitions between them. Confirmed is a known fact of existence of the two major surface wind regimes over the Black Sea i.e., Southern–Western (SW) and Northern–Eastern (NE) and new details on the correlations between the zonal and meridional wind components in each regime are added. A new important finding is that the switch between two regimes occurs quite abruptly at values of NAO index slightly less then zero. It was shown that in weak to moderate positive NAO situation the SW wind regime prevail and wind components are well correlated with the NAO index. The long-term variability of winter-mean SST in the Black Sea is reasonably well correlated with the variability of surface air temperature (SAT), which in turn is highly correlated with the meridional component of surface wind. It is shown that strengthening/weakening of the Southern wind or weakening/strengthening of the Northern wind cause SAT and SST increase/decrease. Finally, a conceptual diagram of NAO impact on the meridional component of the surface wind, SAT and SST is presented.

Coherent Modes of Global SST and Summer Rainfall over China: An Assessment of the Regional Impacts of the 1997–98 El Niño

In this paper, we have identified three principal modes of summertime rainfall variability over China and global sea surface temperature (SST) for the period 1955-1998. Using these modes, we have assessed the impact of the El Nino/La Nina on major drought and flood occurrence over China during 1997-1998. The first mode can be identified with the growth phase of El Nino superimposed on a linear warming trend since the mid-1950s. This mode strongly influences rainfall over northern China. The second mode comprises of a quasi-biennial tendency manifested in alternate wet and dry years over the Yangtze River Valley (YRV) of central China. The third mode is dominated by a quasi-decadal oscillation in eastern China between the Yangtze River and the Yellow River. Using a mode-by-mode reconstruction, we evaluate the impacts of the various principal modes on the 1997 and 1998 observed rainfall anomaly. We find that the severe drought in northern China, and to a lesser degree the flood in southern China, in 1997 is likely a result of the influence of anomalous SST forcing during the growth phase of the El Nino. In addition, rainfall in southern China may be influenced by the decadal or long-term SST variability. The severe flood over the Yangtze River Valley in 1998 is associated with the biennial tendency of basin scale SST during the transition from El Nino to La Nina in 1997-98. Additionally, the observed prolonged drought over northern China and increasing flooding over the YRV since the 1950s may be associated with a long-term warming trend in the tropical Indian and western Pacific ocean. During 1997, the El Nino SST exacerbated the drought situation over northern China. In 1998, the drought appeared to get temporary relief from the La Nina anomalous SST forcing.