Summer Sea Surface Temperature Research Articles

Local and regional variation in kelp loss and stability across coastal British Columbia

Kelp forests are among the most abundant coastal marine habitats but are vulnerable to climate change. The Northeast Pacific has experienced recent large-scale changes in kelp abundance and distribution, but little is known about changes north of the British Columbia (BC)-Washington border. Here, we assessed whether and how floating canopy kelp (Macrocystis pyrifera, Nereocystis luetkeana) distributions have changed in recent decades along the extensive coast of BC. We assembled and analysed available kelp distributional data, comparing snapshots of kelp linear extent from 1.5-3 decades ago (1994-2007) to recently collected data (2017-2021) across 11 different subregions spanning the province. We then leveraged timeseries, where available (n = 7 data sets), to contextualise patterns of change. In aggregate, the data suggest that kelp forests have declined considerably in some parts of the province, but with variable patterns of change across BC. In the warmest areas (southern BC), kelp persistence was negatively correlated with mean summer sea surface temperatures, which at times exceeded known thermal tolerances. In contrast, in northern subregions, top-down control by sea urchins and otters appeared to modulate kelp dynamics, with declines occurring in 2 subregions despite cool ocean temperatures. Timeseries data suggest that many declines occurred around the 2014-2016 marine heatwave, an event associated with sustained warming and altered trophic dynamics. Our results suggest that the extent of BC’s kelp forests has declined in some places in recent decades, but that regional and local-scale factors influence their responses to environmental change.

Investigating extreme marine summers in the Mediterranean Sea

Abstract. The Mediterranean Sea (MS) has undergone significant surface warming, particularly pronounced during summers and associated with devastating impacts on marine life. Alongside the ongoing research on warming trends and marine heatwaves (MHWs), here we address the importance of understanding anomalously warm conditions also on the seasonal timescale. We propose the concept of extreme marine summers (EMSs) and investigate their characteristics in the MS, using sea surface temperature (SST) reanalysis data spanning 1950–2020. We define EMSs at a particular location, as the summers with a mean summer SST exceeding the 95th percentile. A marine summer may become extreme, under various SST substructures. Results show that, in most of the basin, EMSs are formed primarily due to the warmer summer days being warmer than normal. Areas where the warmest (coldest) part of the SST distribution is more variable experience EMSs primarily due to the warmest (coldest) part of the distribution being anomalously warm. MHWs occurring within EMSs are more intense, longer lasting, and more frequent than usual mainly in the northern MS regions. These enhanced MHW conditions occur mainly within the warmest part of the SST distribution. By means of temporal coverage of MHW conditions, a more pronounced occurrence of MHWs in EMSs is found for the central and eastern basin where up to 55 % of MHW days over 1950–2020 fall within EMSs. The role of air–sea heat fluxes in driving EMSs is quantified through a newly proposed metric. Results suggest that surface fluxes primarily drive EMSs in the northern half of the MS, while oceanic processes play a major role in southern regions. Upper-ocean preconditioning also contributes to the formation of EMSs. Finally, a detrended dataset was produced to examine how the SST multi-decadal variability affects the studied EMS features. Despite leading to warmer EMSs basin-wide, the multi-decadal signal does not significantly affect the dominant SST substructures during EMSs. Results also highlight the fundamental role of latent heat flux in modulating the surface heat budget during EMSs, regardless of the long-term trends.

Precursory signals of summer precipitation over southern Central Asia: Combined effect of April soil moisture and sea surface temperature

AbstractThis study investigates the interannual variability of summer precipitation over Central Asia and explores its precursory signals through soil moisture (SM) and sea surface temperature (SST) anomalies. The results reveal that southern Central Asia (SCA) is a crucial SM‐precipitation coupling region where summer precipitation is significantly linked to the preceding April SM in the Turan Plain, between the Caspian Sea and the Tibetan Plateau. The preceding Turan Plain SM (TPSM) anomaly can reflect the ensuing summer SM anomalies in the SCA region due to the persistence of SM. The higher TPSM can stimulate anomalous convective ascent and associated negative geopotential height anomalies over the SCA region, which is favourable for more SCA precipitation (SCAP) during summer. Additionally, Indian and Pacific Ocean SST (IPOS) anomalies can regulate the summer SCAP through ocean and land relay effects. The preceding April can reflect the subsequent summer SST anomalies across the northern Indian Ocean and South China Sea, which trigger a Matsuno‐Gill response and induce anomalous water vapour transport into the SCA region, providing favourable moisture conditions for more SCAP during summer. Apart from such an ocean relay effect, the preceding IPOS can modulate the April TPSM first and then affect the summer SCAP through the land relay effect caused by persistent SM anomalies from April to summer. The combined effect of the preceding TPSM and IPOS on the summer SCAP is more pronounced than the respective effect of either TPSM or IPOS. Incorporating the TPSM signal as a supplementary precursor can enhance the predictive skill of summer SCAP. These findings may provide valuable insights into the reasons and prediction of the variability of summer SCAP.

Warming-induced flowering and fruiting in the seagrass Posidonia oceanica and uncertainties due to context-dependent features

This study explores the impacts of global warming on the reproductive efforts of Posidonia oceanica, a key seagrass species endemic to the Mediterranean Sea. By analyzing data from five areas in Sardinia in February 2023, we have investigated the relationship between thermal descriptors and P. oceanica flowering and fruiting variables. In fact, whether climate change has been affected the distribution of seagrasses by changing their reproductive efforts is still controversial and our findings contribute to this ongoing debate, highlighting a noticeable increase in reproductive events potentially affected by rising temperature. Overall, mean summer sea surface temperature (SST) was positively associated to inflorescence density, presence of living fruits and fruit size; living fruits and fruit size were also influenced positively by the maximum SST within 3 months before sampling (November–February). Both flowering and fruiting were negatively affected by the maximum SST within 1 month before inflorescence observation and mean winter SST, respectively, suggesting that P. oceanica reproductive effort depends on the duration and the temporal context in which the anomaly occurs. However, the high variability between meadows of the same area highlights the need of future studies to focus on the uncertainties related to local factors.

Interannual relationship between the Asian–Pacific Oscillation and summer sea surface temperature in the North Atlantic

Over the last two decades, there has been increasing interest in investigating the connection between the Asian-Pacific Oscillation (APO) and weather and climate on regional and global scales, but the impacts of the APO on sea surface temperature (SST) remains unclear. Using the multisource reanalysis dataset and observed SST data, we evaluated the interannual relationship between the APO and SST in the North Atlantic (NASST) during the period 1979–2016. The results show that there exists a statistically significant positive interannual relationship between APO and NASST and this connection can be attributed to the Rossby wave train that originates in Asia and propagates to Europe, which is triggered by the APO forcing. Further examination revealed that the cloud radiation, air–sea heat exchange and oceanic dynamic process induced by APO are crucial in modulating the interannual variability of the NASST. Additionally, the numerical simulation results from the linear baroclinic model also provide additional evidence for this linkage.

NORWEGIAN SEA HOLOCENE ENVIRONMENTS BASED ON THE FOSSIL MICROALGAE ASSEMBLAGES

Detailed micropaleontological analysis was performed on the sediment core AMK-6142 collected in the deep-sea southwestern part of the Lofoten Basin in the Norwegian Sea. Summer sea-surface temperature for the last 7 cal. ky was reconstructed from dinocyst assemblages using the modern analogue technique (MAT). Sea-surface temperature reconstruction and dinocysts species composition indicate repeated changes in the surface environments during the Middle and Late Holocene. Episodes of cooling and probable displacement of the Arctic Front to the southwestern part of the Lofoten Basin were recorded for 5–7, 1.6–2.1, and 0.1–1.0 cal. ka BP.

Projections of central Arctic summer sea surface temperatures in CMIP6

One of the most dramatic climate responses to future global warming is the near-disappearance of the perennial sea ice cover in the central Arctic Ocean, a phenomenon known as the ice-free summer Arctic. The immediate consequence of an ice-free Arctic would be the surface warming of the central Arctic Ocean, where sea surface temperatures (SSTs) used to be at freezing levels. Through an analysis of climate models participating in the climate model intercomparison project phase-6, this study demonstrates a wide range of responses in the central Arctic SSTs in August–September as a result of the projected ice-free summer Arctic. These responses vary from 0.7 to 8 °C in the shared socioeconomic pathway 2 (SSP2-4.5), referred to as the ‘middle of the road’ scenario, in which socioeconomic and technological trends do not significantly deviate from historical patterns. The extent of the central Arctic sea surface warming in August–September is found to have a loose correlation with the September sea ice extent (SIE), but a stronger connection to the SIE during spring to early summer (May–July), when incoming shortwave radiation is most intense. In certain climate models, the perennial sea ice cover disappears completely in September, causing central Arctic SSTs to rise by 5 °C–8 °C by the end of the 21st century. This leads to a bimodal distribution of annual SSTs. Further analysis reveals a close relationship between mid-summer SSTs in the central Arctic Ocean and preceding winter sea ice thickness (SIT). This underscores the significance of winter SIT in predicting future Arctic surface warming and marine heatwaves.

Natural and Anthropogenic Climate Variability Signals in a 237‐Year‐Long Coral Record From the Philippines

AbstractBoth proxy and model studies conducted to understand anthropogenic warming have revealed historical variations in sea‐surface temperature (SST) since the industrial revolution. However, because of discrepancies between observations and models in the late nineteenth century, the timing and degree of anthropogenic warming remain unclear. In this study, we reconstructed a 237‐year‐long record of SST and salinity using a coral core collected from Bicol, southern Luzon, Philippines, which is located at the northern edge of the western Pacific warm pool. The SST record showed volcanic cooling after several volcanic eruptions, including the 1815 Tambora eruption, but the pattern of change differed. Decadal SST variations at Bicol are connected to Pacific Decadal Variability (PDV). Therefore, it is suggested that the PDV conditions at the time of the eruption may have influenced marine conditions, such as the degree and duration of cooling and/or salinity, after the eruptions. Although there were discrepancies in SST variations among the modeled, observed, and proxy SST data from the late nineteenth to early twentieth centuries, SST data from the late twentieth century showed globally coherent anthropogenic warming, especially after 1976. In particular, summer SST in the northwestern Pacific has become more sensitive to anthropogenic forcing since 1976.

Upper-ocean temperature characteristics in the subantarctic southeastern Pacific based on biomarker reconstructions

Abstract. As remnants of living organisms, alkenones and isoprenoid glycerol dialkyl glycerol tetraether lipids (isoGDGTs) are widely used biomarkers for determining ocean water temperatures from the past. The organisms that these proxy carriers stem from are influenced by a number of environmental parameters, such as water depth, nutrient availability, light conditions, or seasonality, which all may significantly bias the calibration to ambient water temperatures. Reliable temperature determinations thus remain challenging, especially in higher latitudes and for undersampled regions. We analyzed 33 sediment surface samples from the southern Chilean continental margin and the Drake Passage for alkenones and isoGDGTs and compared the results with gridded instrumental reference data from the World Ocean Atlas 2005 (WOA05) and previously published data from an extended study area covering the central and western South Pacific towards the Aotearoa / New Zealand continental margin. We show that for alkenone-derived sea surface temperatures (SSTs), the widely used global core-top calibration of Müller et al. (1998) yields the smallest deviation of the WOA05-based SSTs. On the contrary, the calibration of Sikes et al. (1997), determined for higher latitudes and summer SSTs, overestimates modern WOA05-based SSTs in both the annual mean and summer. Our alkenone SSTs show a slight seasonal shift of ∼ 1 ∘C at the southern Chilean margin and up to ∼ 2 ∘C in the Drake Passage towards austral summer SSTs. Samples in the central South Pacific, on the other hand, reflect an annual mean signal. We show that for isoGDGT-based temperatures, the subsurface calibration of Kim et al. (2012a) best reflects temperatures from the WOA05 in areas north of the Subantarctic Front (SAF). Temperatures south of the SAF are, in contrast, significantly overestimated by up to 14 ∘C, irrespective of the applied calibration. In addition, we used the GDGT [2]/[3] ratios, which give an indication of the production depth of the isoGDGTs and/or potential influences from land. Our samples reflect a subsurface (0–200 m water depth) rather than a surface (0–50 m water depth) signal in the entire study area and show a correlation with the monthly dust distribution in the South Pacific, indicating terrigenous influences. The overestimation of isoGDGT surface and subsurface temperatures south of the SAF highlights the need for a reassessment of existing calibrations in the polar Southern Ocean. Therefore, we suggest a modified Southern Ocean tetraether index (TEX86)-based calibration for surface and subsurface temperatures, which shows a lower temperature sensitivity and yields principally lower absolute temperatures, which align more closely with WOA05-derived values and also OH–isoGDGT-derived temperatures.

Dinoflagellate cysts and benthic foraminifera from surface sediments of Svalbard fjords and shelves as paleoenvironmental indicators

Due to the Arctic amplification effect, the Svalbard archipelago is an important area for studying ongoing environmental changes. However, its marine ecosystem is extremely complex. In this study, we analyze modern assemblages of dinoflagellate cysts (dinocysts) and benthic foraminifera from surface sediment samples around Svalbard. We use multivariate statistical analyses to examine relationships between environmental conditions (summer and winter sea surface temperature and salinity, sea-ice cover, etc.) and both microfossil groups to evaluate their use as proxies for reconstructions of the marine environment in the region. Our results show that the most important factor controlling the environment around Svalbard is the Atlantic Water which mostly impacts the western coast, but its influence reaches as far as the eastern coast of Nordaustlandet. However, on a local scale, such factors as the sea-ice cover, the presence of tidewater glaciers, or even the morphology and hydrology of fjords become increasingly important. We found that two dinocyst species, cysts of Polarella glacialis and Echinidinium karaense, can be considered regional winter drift ice indicators. The relationships between environmental parameters and benthic foraminiferal assemblages are much more difficult to interpret. Although statistical analysis shows a correlation of benthic foraminiferal species with various environmental parameters, this correlation might be somewhat coincidental and caused by other factors not analyzed in this study. Nevertheless, the use of two complementary microfossil groups as (paleo)environmental indicators can provide a more comprehensive picture of the environmental conditions.

Interdecadal Enhancement in the Relationship between the Western North Pacific Summer Monsoon and Sea Surface Temperature in the Tropical Central-Western Pacific after the Early 1990s

Interdecadal Enhancement in the Relationship between the Western North Pacific Summer Monsoon and Sea Surface Temperature in the Tropical Central-Western Pacific after the Early 1990s

Effects of sea ice form drag on the polar oceans in the NEMO-LIM3 global ocean–sea ice model

The surface roughness of sea ice is highly variable because of the diversity of discrete obstacles to the flow present on the sea ice surface. These obstacles result in form drag, an effect poorly accounted for in the calculation of surface fluxes over sea ice in climate models. In this study, we implement in the ocean–sea ice model NEMO-LIM3 a variable formulation of the atmospheric and oceanic neutral drag coefficients over sea ice that includes the form drag effect. We examine the impact of this formulation on the ice cover and ocean surface properties over the past decades in the Arctic and Antarctic. Including form drag in the simulations leads to 10–50cm thinner sea ice in the peripheral Arctic seas and ∼10cm thicker sea ice in the Antarctic ice pack on annual means. Form drag significantly impacts summer sea surface temperatures in the marginal ice zone (+0.5 to +1.5°C in the Arctic and -0.5°C in the Antarctic) and sea surface salinities under the ice cover (+0.52 to +0.89g/kg in both polar regions). The seasonality of the ocean surface stress under sea ice is reversed, with a maximum (minimum) ocean surface stress under sea ice in summer (winter) when including form drag. However, this seasonal reversal is likely too intense in our simulations due to the underestimation of the prescribed mean floe lengths in summer. In the Arctic, the long-term declines in sea ice volume and multi-year ice are associated with decreasing neutral drag coefficients and negative trends in ocean surface stress. In the Antarctic, the trends in the neutral drag coefficients control the increase (decrease) in ocean surface stress in the Weddell and Ross (Bellingshausen and Amundsen) Seas. Form drag results in a 22–38% deeper summer mixed layer under polar sea ice and a year-long 10–25m deeper mixed layer in the Central Arctic. All these impacts on the ocean surface properties demonstrate the relevance of form drag for polar ocean modelling.

The impact of rising temperatures on the prevalence of coral diseases and its predictability: A global meta-analysis.

Coral reefs are under threat from disease as climate change alters environmental conditions. Rising temperatures exacerbate coral disease, but this relationship is likely complex as other factors also influence coral disease prevalence. To better understand this relationship, we meta-analytically examined 108 studies for changes in global coral disease over time alongside temperature, expressed using average summer sea surface temperature (SST) and cumulative heat stress as weekly sea surface temperature anomalies (WSSTAs). We found that both rising average summer SST and WSSTA were associated with global increases in the mean and variability in coral disease prevalence. Global coral disease prevalence tripled, reaching 9.92% in the 25 years examined, and the effect of 'year' became more stable (i.e. prevalence has lower variance over time), contrasting the effects of the two temperature stressors. Regional patterns diverged over time and differed in response to average summer SST. Our model predicted that, under the same trajectory, 76.8% of corals would be diseased globally by 2100, even assuming moderate average summer SST and WSSTA. These results highlight the need for urgent action to mitigate coral disease. Mitigating the impact of rising ocean temperatures on coral disease is a complex challenge requiring global discussion and further study.

Variations in Summer Extreme Hot–Humid Events over Eastern China and the Possible Associated Mechanisms

Abstract This study aimed to explore the changing characteristics of summer, compound, extreme hot–humid events over eastern China in recent decades and the associated underlying mechanisms. Results showed that the summer extreme hot–humid events over eastern China have tended to increase but with strong interannual variability in recent decades. Further analyses indicated that the summer sea surface temperature (SST) anomalies over the northwest Pacific (NW Pacific) and western tropical Pacific, and the May Arctic sea ice concentration (SIC) anomalies are the key elements that are closely connected to the variations in extreme hot–humid events over eastern China. The positive SST anomalies over the NW Pacific in summer, on the one hand, could strengthen the local circulation patterns that lead to the anomalous anticyclonic circulation over eastern China. On the other hand, the positive SST anomalies over the western tropical Pacific excite an anomaly pattern similar to the Pacific–Japan pattern that weakens the westerly jet and enhances the anticyclone circulation anomalies over the upper level of eastern China. Both of them provide favorable conditions for extreme hot–humid events over eastern China with increased moisture and temperatures. The sensitivity experiments by the Community Atmosphere Model, version 5 (CAM5), with SST forcing yield similar influencing processes to the observations. Additionally, the effect of SIC may be potentially responsible for the hot conditions in extreme hot–humid events over eastern China. The signal of declining May SIC could persist to summer and then influence the SST anomalies to its south, which could also produce a beneficial background for extreme hot–humid events to increase over eastern China by exciting the Rossby wave train propagating southeastward across the Mongolia–Lake Baikal region.

Decadal Prediction of the Summer Extreme Precipitation over Southern China

The decadal variability of the summer extreme precipitation over southern China (EPSC) is remarkable, especially for the significant decadal enhancement after the 1990s. The study documented that the summer sea surface temperature (SST) over the North Atlantic and spring sea ice concentration (SIC) over the East Siberian Sea can significantly affect the EPSC. The summer SST over the North Atlantic influences the low-pressure cyclone in the western Pacific by modulating the SST over the tropical Pacific, thus affecting EPSC. A decrease in the SIC of the East Siberian Sea induces a negative Arctic Oscillation, which induces the increased SST over northwest Pacific and the anomalous cyclone over there, in turn, affecting EPSC. Both predictors have a quasi-period of 10–14 years, which provides useful predictive signals for EPSC. The leading 7-year SST and the leading 5-year SIC are chosen to establish the prediction model based on the decadal increment method, which can well predict the EPSC, especially for the shift in the early 1990s. These results provide a clue to the limited predictability of decadal-scale extreme climate events.

Interannual variation of summer sea surface temperature in the Amundsen Sea, Antarctica

This paper investigates the interannual variability of January sea surface temperature (SST) in the Amundsen Sea (AS) during the period 1982–2022. SST in the Pine Island Bay (PIB) is found to exhibit the most significant interannual variation, with a standard deviation up to 0.6°. Composite analysis indicates that, in warmer years, the January SST at PIB is approximately 1° higher on average than that in cooler years, and its variation in warmer (cooler) years corresponds to lower (higher) sea ice concentration (SIC) and more (less) surface heat flux; the latter factor is primarily influenced by the albedo of SIC. Further analysis suggests that variability in January SIC is largely dominated by northward sea ice motion during the previous November (r = −0.82), which is consistent with the presence of a contemporaneous northerly 10 m wind anomaly trigged by the Amundsen Sea Low (ASL). The ASL-associated northerly wind anomaly drives northward sea ice motion, reduces SIC, and thus increases the downward heat flux that ultimately results in warmer SST, and vice versa. This study identifies the possible mechanism of anomalous January SST in the PIB, which could provide an important clue for seasonal forecasts of summer SST in the AS.

What Causes the Arabian Gulf Significant Summer Sea Surface Temperature Warming Trend?

The present study investigated the significant sea surface temperature (SST) warming trend during the summer season over the Arabian Gulf (AG) and its links with the large-scale atmospheric driver, namely, the Atlantic multidecadal oscillation (AMO), from 1900 to 2021. The link between the AMO and the AGs oceanic circulations has received little scientific attention. It has been found that there is a significant spatial positive trend, with a maximum of up to 0.6 °C per decade over the far northern end, while the time series trend shows a significant shift after 1995, with an average value of about 0.36 °C per decade. The spatial trend in the AG is eight times and four times higher than the global value from 1980 to 2005 using HadISST and OISST, respectively. The AMOs significant role in the AGs SST significant warming trend has been confirmed by the spatial and temporal correlation coefficient, which is above 0.50 and 0.48, respectively, with statistical significance at the 99% level. The underlying mechanisms that explained the AMO-related AGs SST decadal variability can be explained as follows: when the AMO is in a positive phase, the surface northwesterly wind weakens, leading to (1) less advection of the relatively cold air masses from Southern Europe to the AG and surrounding areas, (2) less evaporation, and thus less surface cooling (3); thus, this enhances the water masses stratification and decreases the upwelling process, and vice versa occurs for the negative phase. For the air temperature, the positive AMO phase coincides with the occurrence of warm air masses covering all of the Arabian Peninsula, North Africa, and Southern Europe. These processes prove that the AMO is a possible candidate for the AGs SST decadal variability, hence enabling a better evaluation of future climate scenarios for this important region. Our results provide initial insights into the AMO-driven spatiotemporal variability in the SST over the AG and prove that the relation is nonstationary over time. Further analyses are required to explore whether the impacts of the AMO are extended to other oceanic variables such as evaporation rate, heat transport, etc.

Interannual changes of the summer circulation and hydrology in the East China Sea: A modeling study from 1981 to 2015

This study investigated long-term interannual changes in summer circulation and hydrology in the East China Sea (ECS) by performing 35-year high-resolution ocean model simulation from 1981 to 2015. The sea surface temperature (SST) warming trend was considerably weaker in summer than in winter. To the east of the Yangtze Estuary, the interannual variation of SST in summer was mainly dominated by horizontal advection associated with variations in the Taiwan warm current and heat flux in the offshore region north of the Yangtze Estuary. Baroclinic circulation during summer played a crucial role in subsurface mixing. Near the surface, the significant atmospheric wind mode (EOF1) and Kuroshio mode (EOF2) dominate interannual variations in ocean circulation. In the subsurface, local wind around the Tsushima Strait dominated the interannual ocean variation. Anomalous northeasterly winds induced a southwestward pressure gradient due to topographical confinement. These anomalies propagated to the south along the continental shelf through topographic Rossby waves. This study identified two types of anomalous features based on combinations of surface and subsurface EOFs. The combination represents an in-phase contribution between wind and Kuroshio forcings and between the surface and subsurface circulation that enhances the hydrological variability in the ECS. The implication on the relevant biogeochemical and ecological studies in the East China Sea is also very crucial at the interannual time scale.

Southern westerly winds and paleoceanography of the San Jorge Gulf (SW-Atlantic ocean, Argentina) during the last 14,000 years

We use pollen and dinocyst assemblages from three sedimentary sequences of the San Jorge Gulf (SJG) to document the vegetation history of the extra-Andean/eastern Patagonia (Argentina), and the latitudinal variations of the Southern Westerly Wind Belt (SWWB) in relation with ocean changes during the Late Pleistocene and Holocene. Our results suggest that prior to 14 cal ka BP, the vegetation of the SJG was dominated by halophytic taxa probably related to arid conditions in coastal environments. After 14 cal ka BP, pollen data suggest the development of shrub and herb vegetation in the Patagonian steppe then characterized by semi-arid conditions. The 14 cal ka BP transition is marked by increasing Nothofagus pollen abundances, suggesting strong westerlies at the onset of the Antarctic Cold Reversal (ACR). This transition is also marked by the occurrence of marine palynomorphs (dinocysts, organic linings of foraminifers), which relate to sea-level rise. The dinocyst assemblages allowed us to quantitatively estimates changes in summer sea-surface temperature (SST) and annual net primary productivity. Between 14 and 10.8 cal ka BP, which encompasses the glacial termination and the early Holocene, dinocyst assemblages are dominated by Operculodinium centrocarpum (∼82%) and Spiniferites mirabilis (∼8%) that suggest warmer conditions than at present. The transition from early to middle Holocene was marked by high SWWB intensity as suggested by pollen assemblages, and an increase of heterotrophic taxa such as Brigantedinium spp., Echinidinium sp., Dubridinium sp., and the cysts of Polykrikos kofoidii, suggesting increased primary productivity and gradual cooling of surface water. After 4 cal ka BP, pollen data suggest a decrease in the SWWB intensity that correlates with glacier advances in Patagonia and a further decrease in summer SST in the SJG.

Cyclic variability of eastern Bering Sea jellyfish relates to regional physical conditions

Globally, there have been few long-term (>30 years), shelf-wide surveys of jellyfish that have allowed for the examination of how populations might respond to changing climatic and oceanographic conditions. One region where investigation of jellyfish responses to climate variability is possible is the eastern Bering Sea, where jellyfish biomass, primarily that of Chrysaora melanaster, has fluctuated dramatically since 1982, when systematic collections of these medusae began. Our previous investigations of a 27-year time series indicated that the timing of the jellyfish biomass increases and declines coincided with transitions between climatic regimes. In the current study, we used updated jellyfish catch and environmental data from 1982 to 2017 and reran our generalized additive model (GAM) analyses to determine if models using solely physical variables and lag of jellyfish biomass could describe accurately the increases and subsequent decreases observed in this jellyfish biomass index. GAMs hindcasting jellyfish biomass for the period 1982–2017 explained a large fraction of the variance, 92.3 % and 86.4 %, for the southeast (SE) and northwest (NW) portions of the survey area, respectively, using jellyfish biomass in the preceding year and physical variables (SE: ice retreat, sea-surface temperature, wind mixing, wind stress and current displacement; NW: sea-surface temperature, ice cover, wind stress and current displacement). We developed more parsimonious models by calculating the variance inflation factor for each term and dropping highly correlated terms from the models. The resulting GAMs continued to explain a significant portion of the variance in jellyfish biomass, i.e., 78.2 % and 73.5 %, in the southeast and northwest survey areas, respectively. Jellyfish biomass in the SE region was correlated with the jellyfish biomass in the preceding year and with wind mixing, wind stress and current displacement. In the NW region, jellyfish biomass was correlated with biomass from the preceding year, and with summer sea-surface temperature and current displacement. Jellyfish biomass in the eastern Bering Sea did not increase during warm periods, as has been speculated to occur elsewhere. Jellyfish, which are both predators and competitors of fish, appear to be responding to changes in physical conditions and are important indicators of ecosystem change in the eastern Bering Sea. The development of models that use physical parameters, as opposed to biological variables that are often not readily available, is key to predicting jellyfish abundance and their impacts on commercially important species.