Low Sea Surface Temperature Research Articles

Impacts of Changed Ice-Ocean Stress on the North Atlantic Ocean: Role of Ocean Surface Currents

The importance of considering ocean surface currents in ice-ocean stress calculation in the North Atlantic Ocean and Arctic sea ice is investigated for the first time using a global coupled ocean-sea ice model. Considering ocean surface currents in ice-ocean stress calculation weakens the ocean surface stress and Ekman pumping by about 7.7 and 15% over the North Atlantic Ocean, respectively. It also significantly reduces the mechanical energy input to ageostrophic and geostrophic currents, and weakens the mean and eddy kinetic energy by reducing the energy conversion rates of baroclinic and barotropic pathways. Furthermore, the strength of the Atlantic Meridional Overturning Circulation (AMOC), the Nordic Seas MOC, and the North Atlantic subpolar gyre are found to be reduced considerably (by 14.3, 31.0, and 18.1%, respectively). The weakened AMOC leads to a 0.12 PW reduction in maximum northward ocean heat transport, resulting in a reduced surface heat loss and lower sea surface temperature over the North Atlantic Ocean. This reduction also leads to a shrink in sea ice extent and an attenuation of sea ice thickness. These findings highlight the importance of properly considering both the geostrophic and ageostrophic components of ocean surface currents in ice-ocean stress calculation on ocean circulation and climate studies.

Delayed Impact of Indian Ocean Warming on the East Asian Surface Temperature Variation in Boreal Summer

AbstractA significant negative relationship is found between the summer mean north Indian Ocean sea surface temperature (SST) and East Asian surface temperature anomalies. However, the relationship is distinctively different for each month and shows a time-lagged relation rather than a simultaneous one. The north Indian Ocean warming in June is responsible for significant cold anomalies over the region of the Korean Peninsula and Japan (KJ region) that peak in July, exhibiting a 1-month leading role. The SST increase is closely associated with enhanced convective activity in the region in June, but the relationship between SST and resultant precipitation is substantially weakened afterward. This dependency of the precipitation sensitivity on SST anomalies is related to the climatological evolution of SST. The relatively low background SST due to the strengthening of southwesterly monsoons in the late summer can weaken the sensitivity of the precipitation to SST anomalies, yet the background SST in June is strong enough to maintain an increased sensitivity of precipitation. Thus, the Indian Ocean warming in June effectively drives atmospheric Kelvin waves that propagate into the equatorial western Pacific. In the western North Pacific (WNP), the resultant Kelvin wave–induced Ekman divergence triggers suppressed convection and anticyclonic anomalies. The WNP suppressed convection and anticyclonic anomalies move slowly northeastward until they are located near 20°N through the local air–sea interaction, and act as a source of the Pacific–Japan teleconnection. This teleconnection pathway brings clod surface anomalies to the KJ region due to the cyclonic circulation that causes the radiative and horizontal advection.

Spatial and Temporal Distribution of Sea Salt Aerosol Mass Concentrations in the Marine Boundary Layer From the Arctic to the Antarctic

AbstractGlobal warming, increases in sea surface temperatures (SST), and reductions in sea ice may lead to changes in the distribution of global sea salt aerosol (SSA) concentrations, which may in turn affect the global climate. However, there are few global‐scale observations of SSA over marine environments. Here, we report SSA mass concentrations observed along the cruise tracks of the Chinese Polar Research Expedition in summer 2008–2018. We found the following: (1) There are significant differences between SSA concentrations in sea areas at different latitudes, and that of the Arctic Ocean was significantly lower than other sea areas; (2) over the last 10 years, the SSA concentrations in the Bering Sea were significantly higher in 2016 than in 2012, and trends from the Arctic Ocean and Southern Ocean are similar, as both showed a minimum in 2014; (3) the sea‐air temperature differences among the various marine regions studied may contribute to the different distribution of SSA concentrations; (4) sea ice fraction and SST are probably the main factors controlling the interannual changes in SSA concentrations in the Arctic Ocean and Bering Sea, respectively; and (5) The large sea‐air temperature difference in the Southern Ocean may promote the emission of SSA. Therefore, the SST parameterization of GEOS Chem model in the low SST sea area (the Southern Ocean) may have an excessively large effect on suppressing SSA emission resulting in a significant underestimation of the GEOS‐Chem model in the Southern Ocean (−62%).

Assessing Summertime Primary Production Required in Changed Marine Environments in Upwelling Ecosystems Around the Taiwan Bank

The Taiwan Bank (TB) is located in the southern Taiwan Strait, where the marine environments are affected by South China Sea Warm Current and Kuroshio Branch Current in summer. The bottom water flows upward along the edge of the continental shelf, forming an upwelling region that is an essential high-productivity fishing ground. Using trophic dynamic theory, fishery resources can be converted into primary production required (PPR) by primary production, which indicates the environmental tolerance of marine ecosystems. This study calculated the PPR of benthic and pelagic species, sea surface temperature (SST), upwelling size, and net primary production (NPP) to analyze fishery resource structure and the spatial distribution of PPR in upwelling, non-upwelling, and thermal front (frontal) areas of the TB in summer. Pelagic species, predominated by those in the Scombridae, Carangidae families and Trachurus japonicus, accounted for 77% of PPR (67% of the total catch). The benthic species were dominated by Mene maculata and members of the Loliginidae family. The upwelling intensity was the strongest in June and weakest in August. Generalized additive models revealed that the benthic species PPR in frontal habitats had the highest deviance explained (28.5%). Moreover, frontal habitats were influenced by NPP, which was also the main factor affecting the PPR of benthic species in all three habitats. Pelagic species were affected by high NPP, as well as low SST and negative values of the multivariate El Niño–Southern Oscillation (ENSO) index in upwelling habitats (16.9%) and non-upwelling habitats (11.5%). The composition of pelagic species varied by habitat; this variation can be ascribed to impacts from the ENSO. No significant differences were noted in benthic species composition. Overall, pelagic species resources are susceptible to climate change, whereas benthic species are mostly insensitive to climatic factors and are more affected by NPP.

Structure and function of the southeastern Gulf of California ecosystem during low and high sea surface temperature variability

The southeastern Gulf of California is located where two major ocean systems meet: the California Current at the north and the North Equatorial current at the south, however the ecosystem-level effects that have such confluence remain unknown. In this study, we compared the structure and function of this ecosystem between two periods 1994–1997 and 2006–2007. We based the comparison on food web models built with Ecopath with Ecosim (EwE) modeling software and assumed local sea surface temperature anomalies (1993–2009) as an environmental indicator. We analyzed the ecosystem function using indicators estimated by EwE. We performed structural analysis using topological centrality indices to analyze the role of trophic species in the food web. We found that the structure and function of the ecosystem differed among the two periods, which were characterized by two clearly different levels of variation (low variability in 1994–1997 and high variability in 2006–2007). The total biomass, total system throughput, net production of the system, connectance and Finn’s cycling index decreased from 1994–1997 to 2006–2007. The mean transfer efficiency (MTE) revealed that in the period, the energy flow among trophic levels was more efficient. During 2006/07, there was an increase in the ecosystem’s organization, but at the same time, the ecosystem may have been more vulnerable to external perturbations because its resilience decreased. In relation to the structural role of trophic compartments, there were differences in both periods. We found that most groups change their trophic role under different oceanographic conditions. We discuss that the changes in the ecosystem are related to local variability in sea surface temperature.

Individual and combined impacts of ENSO and East Asian winter monsoon on the South China Sea cold tongue intensity

A region of low sea surface temperature (SST) extends southward in the central part of southern South China Sea during boreal winter, which is called the South China Sea cold tongue (SCS CT). The present study investigates the factors of interannual variation of SST in the SCS CT region and explores the individual and combined impacts of El Nino-Southern Oscillation (ENSO) and East Asian winter monsoon (EAWM) on the SCS CT intensity. During years with ENSO alone or with co-existing ENSO and anomalous EAWM, shortwave radiation and ocean horizontal advection play major roles in the interannual variation of the SCS CT intensity. Ocean advection contributes largely to the SST change in the region southeast of Vietnam. In strong CT years with anomalous EAWM alone, surface wind-related latent heat flux has a major role and shortwave radiation is secondary to the EAWM-induced change of the SCS CT intensity, whereas the role of ocean horizontal advection is relatively small. The above differences in the roles of ocean advection and latent heat flux are associated with the distribution of low level wind anomalies. In anomalous CT years with ENSO, low level anomalous cyclone/anticyclone-related wind speed change leads to latent heat flux anomalies with effects opposite to shortwave radiation. In strong CT years with anomalous EAWM alone, surface wind-related latent heat flux anomalies are large as anomalous winds are aligned with climatological winds.

Chronological control and centennial-scale climatic subdivisions of the Last Glacial Termination in the western Mediterranean region

The Last Glacial Termination is marked by changing environmental conditions affected by abrupt and rapid climate oscillations, such as Heinrich Stadial 1 (HS1), which is characterized by extremely low sea surface temperatures (SST) and significant changes in northern hemisphere terrestrial landscape (e.g., vegetation) and human dispersion. Previous studies show that overall cold/dry conditions occurred during HS1, but the lack of high-resolution records precludes whether climate was stable or instead characterized by instability. A high-resolution paleoclimatic record from the Padul wetland (southern Iberian Peninsula), supported by a high-resolution chronology and contrasted with other records from southern Europe and the Mediterranean region, shows 1) that the age boundaries of HS1 in this area occurred at ∼18.0 kyr BP (median age = 17,970 cal yr BP; mean age = 18,030 ± 330 cal yr BP) and ∼15.2 kyr BP (median age = 15,210 cal yr BP; mean age = 15,200 ± 420 cal yr BP) and 2) that climate during HS1 was non-stationary and centennial-scale variability in moisture is superimposed on this overall cold climatic period. In this study, we improve the pollen sampling resolution with respect to previous studies on the same Padul-15-05 sedimentary core and suggest a novel subdivision of HS1 in 7 sub-phases, including: i) 3 sub-phases (a.1-a.3) during an arid early phase (HS1a; ∼18.4–17.2 kyr BP), ii) a relatively humid middle phase (HS1b; ∼17.2–16.9 kyr BP), and iii) 3 sub-phases (c.1-c.3) during an arid late phase (HS1c; ∼16.9–15.7 kyr BP). This climatic subdivision is regionally supported by SST oscillations from the Mediterranean Sea, suggesting a strong land-sea coupling. A cyclostratigraphic analysis of pollen data between 20 and 11 kyr BP indicates that the climate variability and the proposed subdivisions characterized by ∼2000 and ∼800-yr periodicities could be related to solar forcing controlling climate in this area.

Impact of environmental changes on the fishery of motorized and non-motorized sub-sectors of the upwelling zone of Kerala, southeastern Arabian sea

The marine waters of Kerala state along the southwest coast of India are among the most productive upwelling regions in the southeastern Arabian Sea. Analyses were made to assess the impact of environmental changes on the marine fish catch using motorized and non-motorized craft operating off the coast. The catch per unit effort (CPUE) of total landings, OBGN (outboard gillnet), OBTN (outboard trawlnet), NM (non-motorized) crafts, as well as the catch of 5 major fish resources Indian mackerel, lesser sardines, Stolephorus spp., scads, and penaeid prawns were obtained. Sea surface temperature (SST), chlorophyll, salinity, rainfall, sea level anomaly, multivariate ENSO index, dipole mode index, local temperature anomaly, degree heating month (DHM), degree cooling month (DCM) and surface currents were used as variables to investigate the relationship between environment and fishery. Principal component analysis was used to select the minimum data set and GAM (Generalized additive model) was used to detect the influence of the environment on the fisheries. The adjusted R2 value of the GAM was 0.68, taking the CPUE of the total landings as the response variable. For the case of the selected fish resources, the adjusted R2 value of the GAM was 0.73 for penaeid prawns, followed by Stolephorus spp. (0.44), scads (0.33), lesser sardines (0.31), and Indian mackerel (0.25). Considering the CPUE as the response variable for the GAM also returned high adjusted R2 values for fishing method (OBGN = 0.59, OBTN = 0.53 and NM = 0.31). SST, chlorophyll, rainfall, salinity, yearly DCM and surface currents all had significant influences on the marine fisheries along the Kerala coast. Lower SST, high salinity and rainfall promote the fisheries of both small pelagics and large pelagic groups like scads. Along with the negative relationship between SST and fishery, the present analyses also indicate a positive relationship with yearly DCM, which clearly indicates that the warming of coastal waters has a negative impact on fisheries along the Kerala coast. From these results, we find that ocean currents can play a crucial role in fish recruitment in the coastal waters of Kerala. Primary production, the key factor for marine fishery production, was found to be controlled by environmental factors like SST and currents. These results point to the vulnerability of the small-scale fisheries sector of the tropical upwelling zone to increasing SST and climate change.

Planktic foraminiferal δ18O values indicate precipitation variability in the southeastern South China Sea over the last 175 ka BP

The South China Sea (SCS) is an important research area of the tropical water cycle and an important pathway by which the Asian monsoon transports water vapor and heat from the tropical ocean to the Asian continent, yet its response to low-latitude tropical processes is poorly resolved. Here, we report high-resolution records of the oxygen isotopes (δ18O) of planktic Globigerinoides ruber and Globorotalia menardii at different depths and Mg/Ca ratios from a core in the southeastern SCS over the last 175 ka BP to discuss the variability of sea surface temperature (SST) and salinity (SSS) patterns, which can provide insights into understanding SCS hydroclimate dynamics. The records show that SST was characterized by glacial-interglacial cycles largely controlled by ice volume and orbital insolation-driven changes in monsoon circulation. Several short high-frequency intervals of high SST in the glacial periods and low SST in the stadial periods corresponded to variations involving enhanced winter or summer monsoons. The variation in δ18O is obviously influenced by monsoon-driven SSS. Although the δ18O values in different areas of the SCS were similar, the comparison shows that the δ18O values in the study area were lower than those in the northern SCS but higher than those in the southern SCS, appearing to reveal the tropical water cycle process of evaporation, transmission and rainfall in the SCS. The negative deviation in δ18O peaks indicated heavy precipitation in the southeastern SCS caused by an enhanced convection intensity and strengthened summer monsoons. A valuable set of surface and subsurface Δδ18OG.r-G.m (Δδ18OG. ruber - Δδ18OG. menardii) records proved that more negative δ18O shifts must be closely related to the surface seawater environment. However, negative shifts in δ18O were controlled by different mechanisms during the glacial and interglacial periods. In the interglacial periods, the northward shift of the intertropical convergence zone (ITCZ) and summer solar insolation played a key role in precipitation, whereas in the glacial periods, El Niño events and differences in the thermal properties between the sea and land dominated.

Improvement of SMAP sea surface salinity in river-dominated oceans using machine learning approaches

ABSTRACT Sea salinity is one of the indicators of the global water cycle and affects the surface and deep circulation of the ocean. While passive microwave satellite sensors have been used to monitor sea surface salinity (SSS), the uncertainties from radio frequency interference (RFI) and low sea surface temperature often result in large errors, especially in river-dominated coastal seas. This study investigated the improvement of the Soil Moisture Active Passive (SMAP) SSS over five river-dominated oceans over the globe using three machine learning approaches (i.e., random forest (RF), support vector regression (SVR), and artificial neural network (ANN)). Four SMAP products and four ancillary data used in the SMAP SSS retrieval algorithm were used as input variables to the machine learning models. The results showed that all models improved the SMAP SSS product by up to 28% reduced in the root mean square error (RMSE) for validation, and RF yielded better performance than SVR and ANN. The calibration and validation RMSEs by RF were 0.203 and 0.556 practical salinity unit (psu), while those of SMAP SSS were 0.774 psu. The improved SSS well captured the spatiotemporal patterns of SSS for not only low but also high salinity water for all five regions. The proposed approach can be used to operationally improve the global SMAP SSS product including other coastal areas and the near Polar regions in the future.

Sea surface temperature (SST) anomalies of the Yellow and East China Seas in July of 2020

With the global warming, the long term variations of sea surface temperature and its anomalies in the Yellow and East China Seas, especially for the July of 2020 due to the abnormally torrential rain along Changjiang/Yangtze River Valley, have been investigated based on the Merged Satellite and In-situ Data Global Daily sea surface temperature (MGDSST) provided by the Japan Meteorological Agency (JMA) using the methods of composite and correlation analyses. The results suggest, contrary to warming anomalies in the North-western Pacifica Ocean, the sea surface temperature in the East China Sea is cooler around 0.5°C and that in the East China Sea is cooler around 1.3°C than the normal values. The sea surface temperatures approach the extreme low value in the Yellow Sea and East China Sea in July, and warm up to the normal year in August. In addition, the south-westerly summer monsoon over this region, is proposed to contribute the transport of Kuroshio and its pathway. The obvious westerly wind anomalies, correspond to the lower sea surface temperature over the Yellow and East China Seas in July of 2020, leads to a clear less heat advection from Kuroshio to this region. Further, the low sea surface temperature, leading a downward air motion with a convergence at near sea surface level, is helpful for the enhance of the westerly wind anomalies until the strong surface heat flux in August. This study suggests that the local horizontal circulation advection and net heat flux are also dominated on the heat content of the East China waters. Further quantitative studies are worth conducting.

Climate-related changes in seasonal habitat pattern of Sthenoteuthis oualaniensis in the South China Sea

ABSTRACT A habitat suitability index model (HSI) was established to examine seasonal habitat pattern of Sthenoteuthis oualaniensis in the South China Sea and assessed the impacts of the El Niño event on habitat variations based on sea surface temperature (SST), chlorophyll-a (Chla) and sea surface height (SSH). Environmental conditions and habitat patterns showed significant seasonal and spatial variations. Spatial pattern of favorable environmental conditions played important roles in regulating the ranges and longitudinal and latitudinal distributions of suitable habitats (areas with HSI≥0.6) of S. oualaniensis across seasons. Significant positive correlation was found between SST and HSI, whereas negative relationship was revealed between HSI and Chla as well as SSH by correlation analysis. Comparing to normal climate condition in spring 2014, the El Niño events in spring 2015 and 2016 yielded lower SST and higher Chla and SSH, which were unfavorable for the formation of high-quality habitats. Favorable ranges of environmental conditions showed decreasing trend from spring 2014 to 2016. Consequently, the suitable habitats in spring 2015 and 2016 largely contracted and became discontinuity. Our findings indicated that seasonal habitat patterns of S. oualaniensis in the South China Sea were strongly affected by the El Niño events and local environmental conditions.

Spatial Distribution of Extremely Low Sea-Surface Temperature in the Global Ocean and Analysis of Data Visualization in Earth Science Textbooks

Spatial Distribution of Extremely Low Sea-Surface Temperature in the Global Ocean and Analysis of Data Visualization in Earth Science Textbooks

Estimating the spawning ground of Pacific saury Cololabis saira by using the distribution and geographical variation in maturation status of adult fish during the main spawning season

AbstractWe analyzed distribution and differences in body length, age, and maturation rate of Pacific saury Cololabis saira in the western North Pacific Ocean, during the main spawning season (winter), to locate its spawning ground. Sampling was conducted in the coastal area north of the Kuroshio axis (CA), the offshore area of the southern Japanese archipelago (SA), and the area east of the Honshu Island (EA) from 1996 to 2017. Higher densities of Pacific saury were widely observed on or just north (within 100–200 km) of the axis of the Kuroshio and the Kuroshio Extension currents. Body length, age composition, and sea‐surface temperature (SST) differed across the studied areas, with larger fish (>250 mm knob length, mainly age‐1) dominating at higher SST (16–21°C) in the SA and smaller fish (<250 mm knob length, age‐0) dominating at lower SST (14–16°C) in the EA. In the CA, both SST and body length values were in between those in the SA and EA. The area where matured Pacific saury were collected was broadly distributed in the study area, except for the CA and a part of the Transition zone where the SST was low and mean body length was short. This study suggests that the main spawning ground during winter, where the area of high density and high maturation rate overlap, is formed on or just north of the Kuroshio and the Kuroshio Extension axis.

Simulation study on the effect of atmosphere-ocean-wave interactions on Typhoon Rammasun (2014) in the South China Sea

The paper implemented a “standard” coupling system in the South China Sea without any further development avoiding to add a new parameterization on ocean-atmosphere-wave interaction. The sea and the waves influenced tropical cyclone (TC) through the interaction between the air and sea fluxes. The performance of the fully coupled atmosphere-ocean-wave model is overall better that of the uncoupled model, especially for track and intensity. However, the simulated TC was weaker using coupled model and the weakest using the fully coupled atmosphere-ocean-wave model. There are two main reasons for the weakening of simulated TC using coupled model: (1) Lower sea surface temperature caused by the TC reduced the sensible and latent heat fluxes from the ocean to atmosphere, leading to the weakened TC. (2) The increased surface roughness of the sea waves caused by the TC reduced the wind speed over the strong-wind area while increased it over the low-wind area, which further weakened the TC.Sea-air fluxes have strong effects on the structural characteristics of TC. Heat fluxes simulated by coupled model were distributed more asymmetrically, which strengthened the asymmetry of the TC. Strong-wind areas were corresponding to the area with large sea-air fluxes Differences in temperature between atmosphere and ocean directly determine the transporting direction of the sensible heat flux. To the rear side of the TC, sensible heat fluxes occur in the atmosphere and transport to the ocean; while at the front of the TC, sensible heat fluxes occur in the ocean and transport to the atmosphere.

Change Points Detected in Decadal and Seasonal Trends of Outlet Glacier Terminus Positions across West Greenland

We investigated the change in terminus position between 1985 and 2015 of 17 marine-terminating glaciers that drain into Disko and Uummannaq Bays, West Greenland, by manually digitizing over 5000 individual frontal positions from over 1200 Landsat images. We find that 15 of 17 glacier termini retreated over the study period, with ~80% of this retreat occurring since 2000. Increased frequency of Landsat observations since 2000 allowed for further investigation of the seasonal variability in terminus position. We identified 10 actively retreating glaciers based on a significant positive relationship between glaciers with cumulative retreat >300 m since 2000 and their average annual amplitude (seasonal range) in terminus position. Finally, using the Detecting Breakpoints and Estimating Segments in Trend (DBEST) program, we investigated whether the 2000–2015 trends in terminus position were explained by the occurrence of change points (significant trend transitions). Based on the change point analysis, we found that nine of 10 glaciers identified as actively retreating also underwent two or three periods of change, during which their terminus positions were characterized by increases in cumulative retreat. Previous literature suggests potential relationships between our identified change dates with anomalous ocean conditions, such as low sea ice concentration and high sea surface temperatures, and our change durations with individual fjord geometry.

Spatio-temporal variability of temperature and chlorophyll-a concentration of sea surface in Bali Strait, Indonesia

Abstract. Wijaya A, Zakiyah U, Sambah AB, Setyohadi D. 2020. Spatio-temporal variability of temperature and chlorophyll-a concentration of sea surface in Bali Strait, Indonesia. Biodiversitas 21: 5283-5290. The Bali Strait is influenced by seasonal and inter-annual systems. El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are climate variabilities that affect water conditions. The knowledge about influence of ENSO and IOD variations on the fertility of waters in the Bali Strait is still lacking. The purpose of this study was to determine the effect of seasonal and inter-annual variability on the variability of Sea Surface Temperature (SST) and Sea Surface Chlorophyll-a (SSC) in the Bali Strait. This study applied SST and SSC data collected from the Aqua/Terra MODIS satellite, as well as the ENSO and IOD indices during March 2000-December 2019. The results described that the effect of ENSO on SST and SSC was low and IOD on SST and SSC was quite high. The effect was quite high between IOD and SST anomaly of-0.401. Seasonal variations indicate the abundance of high SSC and low SST in the southeast monsoon (JJA) which characterizes upwelling. Meanwhile, in the northwest monsoon (DJF), SSC was low and SST was high which characterizes downwelling. This condition cannot separate from the monsoonal process that occurred in the Bali Strait. The inter-annual variation showed that in the strong El Nino period and IOD (+) triggers a negative SST anomaly and a positive SSC results in strong upwelling, while in the strong La Nina period and strong IOD (-) triggers a positive SST anomaly and a negative SSC results in downwelling. The inter-annual variability of SSC influenced by IOD rather than ENSO. This condition indicates that the ENSO/IOD event changes the period of SSC concentration.

Variability of Sedimentation Processes in Northern Part of East Novaya Zemlya Trough in the Anthropocene

The lithological and mineralogical characteristics of sea surface sediments, composition of microfossils, contribution of organic matter, and element composition have been studied in a core from the northern part of East Novaya Zemlya Trough. Sedimentation rates were calculated based on the radioisotopes 210Pb and 137Cs. Lithological, biogeochemical, and geochemical studies showed a low variability of the sedimentation conditions over the last 250 years. However, even small changes in microfossils, as well as lithological and geochemical parameters, make it possible to trace some short-term climate changes in this area, probably controlled by atmospheric circulation. The core shows a clear binomial structure, reflecting changes in sedimentation at the end of the Little Ice Age (LIA) and afterward. For the northern part of the East Novaya Zemlya Trough, low sea surface temperatures and an increase in the duration of ice cover at the end of the LIA in the 1780s−1810s have been reconstructed. Since the 1810s, the hydrodynamic activity of water masses intensified sharply due to glacier melting (especially after the 1840s). In addition, an increase in sea surface temperatures can be assumed, except for the cooling of the 1910s. Later, circulation of water masses increased, contributing to the supply of terrigenous material to the deep parts of the trough.

Highly variable taxa-specific coral bleaching responses to thermal stresses

Complex histories of chronic and acute sea surface temperature (SST) stresses are expected to trigger taxon- and location-specific responses that will ultimately lead to novel coral communities. The 2016 El Niño-Southern Oscillation provided an opportunity to examine large-scale and recent environmental histories on emerging patterns in 226 coral communities distributed across 12 countries from East Africa to Fiji. Six main coral communities were identified that largely varied across a gradient of Acropora to massive Porites dominance. Bleaching intensity was taxon-specific and was associated with complex interactions among the 20 environmental variables that we examined. Coral community structure was better aligned with the historical temperature patterns between 1985 and 2015 than the 2016 extreme temperature event. Additionally, bleaching responses observed during 2016 differed from historical reports during past warm years. Consequently, coral communities present in 2016 are likely to have been reorganized by both long-term community change and acclimation mechanisms. For example, less disturbed sites with cooler baseline temperatures, higher mean historical SST background variability, and infrequent extreme warm temperature stresses were associated with Acropora-dominated communities, while more disturbed sites with lower historical SST background variability and frequent acute warm stress were dominated by stress-resistant massive Porites corals. Overall, the combination of taxon-specific responses, community-level reorganization over time, geographic variation, and multiple environmental stressors suggest complex responses and a diversity of future coral communities that can help contextualize management priorities and activities.

Geographic variation in feeding of Pacific saury Cololabis saira in June and July in the North Pacific Ocean

AbstractGut contents of Pacific saury Cololabis saira during their feeding migration through a transition zone between subtropical and subarctic waters in the North Pacific Ocean are reported. Geographic changes in feeding habits and preferences are described for the months of June and July, for the years 2012, 2016, and 2017. Pacific saury prey comprised 27 taxa. Cluster analysis based on numerical abundance of these prey taxa in guts indicated six Pacific saury feeding types (A to F) existed. Of these, types A–E occurred in low sea surface temperature waters (<ca 14°C). Gut content weight and gut fullness index were greater in types A, B, and E, with copepods Neocalanus plumchrus/flemingeri and/or N. cristatus contributing highly to carbon‐base weight. Although small euphausiids occurred in guts, guts were also often empty, suggesting feeding was less active at higher sea surface temperatures (>ca 14°C). Feeding patterns reveal N. plumchrus/flemingeri tended to be important prey species in areas west of ca 175°E, whereas Pacific saury feed mainly and selectively on N. cristatus in eastern areas, indicating a longitudinal difference in the trophic pathway from zooplankton prey to Pacific saury. These spatial differences in trophic pathways improve our understanding of nutritional intake in the commercially important Pacific saury during its feeding migration, and the effects this might have on fish size and weight, and associated commercial value.