Warm Water Intrusion Research Articles

Characterizing the influence of Atlantic water intrusion on water mass formation and phytoplankton distribution in Kongsfjorden, Svalbard

Warm water intrusion into Arctic fjords is increasingly affecting polar ecosystems. This study investigated how Atlantic water intrusion and tidewater glacial melting impacted water mass formation and phytoplankton distribution in Kongsfjorden, Svalbard. Field data were collected over a 2-week period during the height of the melt season in August 2014 and were contextualized within an 18-year regional MODIS satellite record. Since 1998, intruding waters have warmed by 4–5.5 °C, which has prevented sea ice formation and changed the characteristics of fjord bottom waters. Modeled light fields suggest that suspended sediment in this glacial meltwater has reduced the euphotic zone close to the ice face, contributing to lower phytoplankton concentrations in both persistent and intermittently sediment-laden meltwater plumes. However, measurements collected close to terrestrially terminating glaciers indicate that turbidity is significantly lower in the meltwater plumes, resulting in deep euphotic zones and high phytoplankton concentrations. The results of this study support a three-part conceptual model of the effects of warm-water intrusion on water mass formation and primary production within 10 km of tidewater glaciers. Initially, warm water intrusion reduces sea ice coverage, which increases the euphotic depth and increases phytoplankton biomass. Warm water intrusions may also result in increased melting of tidewater glaciers, enhanced sediment release, reduction in euphotic depth and reduction in phytoplankton biomass. Ultimately, as tidewater glaciers retreat and become terrestrially terminating, the sediment load decreases, the euphotic zone again increases, and phytoplankton biomass increases.

Development of a new operational system for monitoring and forecasting coastal and open-ocean states around Japan

We developed a new system to monitor and forecast coastal and open-ocean states around Japan for operational use by the Japan Meteorological Agency. The system consists of an eddy-resolving analysis model based on four-dimensional variational assimilation and a high (2-km) resolution forecast model covering Japanese coastal areas that incorporates an initialization scheme with temporal and spatial filtering. Assimilation and forecast experiments were performed for 2008 to 2017, and the results were validated against various observation datasets. The assimilation results captured well the observed variability in sea surface temperature, coastal sea level, volume transport, and sea ice. Furthermore, the volume budget for the Japan Sea was significantly improved by the use of the 2-km resolution forecast model compared with the 10-km resolution analysis model. The forecast results indicate that this system has a predictive limit longer than 1 month in many areas, including in the Kuroshio current area south of Japan and the southern Japan Sea. In the forecast results of case studies, the 2017 Kuroshio large meander was well predicted, and warm water intrusions accompanying Kuroshio path variations south of Japan were also successfully reproduced. Sea ice forecasts for the Sea of Okhotsk largely captured the evolution of sea ice in late winter, but sea ice in early winter included relatively large errors. This system has high potential to meet operational requirements for monitoring and forecasting ocean phenomena at both meso- and coastal scales.

Spatial heterogeneity of seasonal phytoplankton blooms in a marginal sea: physical drivers and biological responses

Abstract Satellite and in situ observations are used in this study to examine spatial heterogeneity in the timing and magnitude of phytoplankton blooms in relation to local and remote physical processes in the Yellow Sea (YS), a marginal sea in the northwestern Pacific Ocean. Satellite ocean colour data reveal that annual chlorophyll maximums vary significantly in both timing and magnitude over different subregions of the YS. Strong summer blooms were found off estuary regions, and widespread spring blooms were found in the central trough. Localized autumn and winter peaks were found in small patches around Jeju Island and in nearshore regions. A statistical analysis of in situ measurements of the western YS suggests that variability in hydrographic properties could explain most of the spatial heterogeneity observed in both bloom timing and magnitude. The spatial heterogeneity of hydrographic properties, such as stratification and nutrient availability, are controlled by a suite of physical forcings, including the extent of the YS Cold Water Mass, river discharge, warm slope water intrusion, and seasonal warming/cooling. Our results imply that the spatial heterogeneity of marginal seas must be carefully considered when assessing phytoplankton responses in the context of climate change, because of the complexity of underlying mechanisms.

The spatial distribution of phytoplankton pigments in the surface sediments of the Kongsfjorden and Krossfjorden ecosystem of Svalbard, Arctic

Kongsfjorden–Krossfjorden twin fjord ecosystem in Svalbard (Arctic), is facing enhanced warm Atlantic water intrusion from ocean as well as intensified melting from glaciers. It is an interesting ecosystem to study phytoplankton productivity under the two opposing processes. For phytoplankton productivity, pigments are used as potential photosynthetic biomass indicators and taxonomic biomarkers. However, due to labile nature of pigments, degradation — preservation distribution must be investigated to form essential framework for biomarker studies. With this motivation, we have undertaken the present work to study the spatial distribution of surface sedimentary pigments in the twin-fjord ecosystem. The pigments were analysed using high-performance liquid chromatography coupled with diode array detector. A total of fifteen pigments were identified, which belonged to different classes — chlorophylls, pheopigments and carotenoids. Chlorophyll-a and pheophorbide-a were major pigments with concentration up to 700–800 ng g−1 dry weight of sediment. Among carotenoids, fucoxanthin, diatoxanthin and prasinoxanthin were abundant with maximum concentration recorded up to 400–600 ng g−1 dry weight. The distribution of the pigments varied significantly between the two fjords as well as in different regions of the fjord. Most of the pigments were significantly high in their concentration at Krossfjorden stations. Within Kongsfjorden, outer region showed higher concentration of pigments than inner. However, preservation was lesser for the outer fjord pigments than inner as confirmed by various pigment indices. Further, the overall distribution of phytoplankton communities derived from taxonomic biomarker pigments in Kongsfjorden–Krossfjorden sediments, was coherent with that of water during spring and summer. The distribution was dominated by diatoms, dinoflagellates, prasinophytes and prymnesiophytes. The surface sedimentary pigments were found capable of providing information about phytoplankton biomass and composition under environmental conditions existing in the region.

Seasonality of Warm Water Intrusions Onto the Continental Shelf Near the Totten Glacier

AbstractWarm Modified Circumpolar Deep Water (MCDW) from the Southern Ocean drives rapid basal melt of the Totten Ice Shelf on the Sabrina Coast (East Antarctica), affecting the mass balance of the grounded Totten Glacier. Recent observations show that MCDW intrudes onto the continental shelf through a depression at the shelf break. Here we investigate such intrusions by combining (1) new oceanographic and bathymetric observations collected for two consecutive years by profiling floats in the depression south of the shelf break, (2) oceanographic measurements collected by conductivity‐temperature‐depth‐instrumented seals on continental slope, and (3) an ocean model. The depression provides a pathway for persistent inflow of warm (0‐1°C) MCDW to the inner shelf. In austral autumn and early winter MCDW intrusions were up to 0.5°C warmer and were ~75 m thicker than in spring and summer. The seasonality of the flow on the continental slope explains the seasonality of the intrusions. The MCDW layer on the continental slope is warmer and thicker to the east of the depression than to the west. In autumn and early winter a strong, top‐to‐bottom westward current (Antarctic Slope Current) transports the warmer and thicker MCDW layer along the slope and is diverted poleward at the eastern entrance of the depression. A bottom‐intensified eastward current (Antarctic Slope Undercurrent) develops in other months, allowing cooler and thinner intrusions to enter the depression from the west. Our study illustrates how circulation on the Antarctic slope regulates the ocean heat delivery to the continental shelf and ultimately to the ice shelves.

Barotropic Kelvin Wave‐Induced Bottom Boundary Layer Warming Along the West Antarctic Peninsula

AbstractIntrusions of warm circumpolar deep water onto the Antarctic continental shelf are thought to drive accelerated loss of Antarctic glacial ice mass by triggering melt at the ice shelf grounding line. However, the mechanisms responsible for driving on‐shelf circumpolar deep water intrusions are not well understood. Here we examine how sea surface height (SSH) anomalies propagating around the Antarctic coastline as coastal‐trapped waves can drive warm water intrusions through changes in bottom Ekman transport. A wind perturbation motivated by the recent intensification and poleward shift of the southern annular mode during its positive phase is applied over Eastern Antarctica between 20°E and 120°E in two global ocean sea‐ice models (1/4° and 1/10°) and a single‐layer shallow water model. The changes in winds generate a drop in coastal SSH that propagates around Antarctica as a barotropic Kelvin wave. The SSH drop is accompanied by a barotropic flow, which alters the bottom stress, generating an onshore transport of warm water wherever thermal gradients are favorable. We estimate the resulting anomalous bottom Ekman flow and use temperature gradients calculated from the Southern Ocean State Estimate, along with the 1/4° and 1/10° models, to evaluate the resultant heat advection. We find that this mechanism can drive warming of up to 0.7 °C along the West Antarctic Peninsula within a year, depending on the mean state of the cross‐shelf temperature gradient and the barotropic flow strength. Over longer time scales, warming eventually ceases due to saturation of the SSH field and arrest of the Ekman transport by buoyancy forces.

Frontogenesis of the Angola–Benguela Frontal Zone

Abstract. A diagnostic analysis of the climatological annual mean and seasonal cycle of the Angola–Benguela Frontal Zone (ABFZ) is performed by applying an ocean frontogenetic function (OFGF) to the ocean mixing layer (OML). The OFGF reveals that the meridional confluence and vertical tilting terms are the most dominant contributors to the frontogenesis of the ABFZ. The ABFZ shows a well-pronounced semiannual cycle with two maximum (minimum) peaks in April–May and November–December (February–March and July–August). The development of the two maxima of frontogenesis is due to two different physical processes: enhanced tilting from March to April and meridional confluence from September to October. The strong meridional confluence in September to October is closely related to the seasonal southward intrusion of tropical warm water to the ABFZ that seems to be associated with the development of the Angola Dome northwest of the ABFZ. The strong tilting effect from March to April is attributed to the meridional gradient of vertical velocities, whose effect is amplified in this period due to increasing stratification and shallow OML depth. The proposed OFGF can be viewed as a tool to diagnose the performance of coupled general circulation models (CGCMs) that generally fail at realistically simulating the position of the ABFZ, which leading to huge warm biases in the southeastern Atlantic.

Depth-Dependent Environmental Drivers of Microbial Plankton Community Structure in the Northern Gulf of Mexico.

The Gulf of Mexico (GoM) is a dynamic marine ecosystem influenced by multiple natural and anthropogenic processes and inputs, such as the intrusion of warm oligotrophic water via the Loop Current, freshwater and nutrient input by the Mississippi River, and hydrocarbon inputs via natural seeps and industrial spills. Microbial plankton communities are important to pelagic food webs including in the GoM but understanding the drivers of the natural dynamics of these passively distributed microorganisms can be challenging in such a large and heterogeneous system. As part of the DEEPEND consortium, we applied high throughput 16S rRNA sequencing to investigate the spatial and temporal dynamics of pelagic microbial plankton related to several environmental conditions during two offshore cruises in 2015. Our results show dramatic community shifts across depths, especially between photic and aphotic zones. Though we only have two time points within a single year, observed temporal shifts in microbial plankton communities were restricted to the seasonally influenced epipelagic zone (0–200 m), and appear mainly driven by changes in temperature. Environmental selection in microbial plankton communities was depth-specific, with variables such as turbidity, salinity, and abundance of photosynthetic taxa strongly correlating with community structure in the epipelagic zone, while variables such as oxygen and specific nutrient concentrations were correlated with community structure at deeper depths.

Contrasting Hydrological Controls on Bed Properties During the Acceleration of Pine Island Glacier, West Antarctica

AbstractIn the Amundsen sector of West Antarctica, the flow of glaciers accelerates when intrusion of warm ocean water onto the continental shelf induces strong melting beneath ice shelves and thinning near the glaciers' grounding line. Predicting the future of these glaciers is, however, hindered by a poor understanding of the dynamical processes that may exacerbate, or on the contrary modulate, the inland ice sheet response. This study seeks to investigate processes occurring at the base of Pine Island Glacier through numerical inversions of surface velocities observed in 1996 and 2014, a period of time during which the glacier accelerated significantly. The outputs show that substantial changes took place in the basal environment, which we interpret with models of undrained subglacial till and hydrological routing. The annual basal melt production increased by 25% on average. Basal drag weakened by 15% over nearly two thirds of the region of accelerated flow, largely due to the direct assimilation of locally produced basal meltwater into the underlying subglacial sediment. In contrast, regions of increased drag are found to follow several of the glacier's shear margins and furthermore to coincide with inferred hydrological pathways. We interpret this basal strengthening as signature of an efficient hydrological system, where low‐pressure water channels have reduced the surrounding basal water pressure. These are the first identified stabilization mechanisms to have developed alongside Pine Island ice flow acceleration. Indeed, these processes could become more significant with increased meltwater availability and may limit the glacier's response to perturbation near its grounding line.

What caused the record‐breaking warming in East China Seas during August 2016?

The East China Seas (ECS) encountered its warmest monthly mean sea surface temperature (SST) in August 2016, based on the high‐resolution satellite SST product (1982–2016). The area‐averaged monthly SST over the ECS (28°–39°N, 120°–130°E) reached up to 28.3 °C, 2 °C above normal that exceeds two times of SD. The isotherms of 28.5 and 30 °C extended to 36° and 32°N, respectively, both reaching their unprecedented northernmost locations. The heat budget analysis indicated that this extreme warming event in the ECS was predominantly attributable to the combined effects of oceanic advection (0.18 °C, ~24%) and net heat flux (0.44 °C, ~58%), with the latter being the dominant contributor. Further, the extreme ECS warming is induced by the strong adiabatic descent motion with increased downward solar radiation due to the anomalous anticyclonic circulation over the north western Pacific, which is closely linked to the negative phase of the Indian Ocean Dipole (IOD) with robust heating over the tropical eastern Indian Ocean and western Pacific. Additionally, the anticyclonic circulation anomalies promoted the intrusion of warm water of the Kuroshio across the ECS shelf, which also contributed to the forming of enhanced ECS warming. It is further found that most of the ECS warming events can be explained by the precursor signals of negative IOD with 1–3 months ahead, which have important implications for prediction.

The Springtime Influence of Natural Tropical Pacific Variability on the Surface Climate of the Ross Ice Shelf, West Antarctica: Implications for Ice Shelf Thinning

Observational records starting in the 1950s show West Antarctica is amongst the most rapidly warming regions on the planet. Together with increased intrusions of warm circumpolar deep water (CDW) onto the continental shelf due to local wind forcing (the primary mechanism in recent decades), this has resulted in enhanced surface and basal melting of floating ice shelves and an associated acceleration and thinning of West Antarctic outlet glaciers, increasing the rate of global sea level rise. In this study, it is shown that during the austral spring season, significant surface warming across West Antarctica has shifted westward to the Ross Ice Shelf in recent decades in response to enhanced cyclonic circulation over the Ross Sea. These circulation changes are caused by a Rossby wave train forced by increasing sea surface temperatures in the western tropical Pacific, which is tied to the springtime shift of the Interdecadal Pacific Oscillation (IPO) to its negative phase after 1992. While the local wind trends enhance warm air advection and surface warming across the Ross Ice Shelf, the strong easterly component of the wind trends reduces the likelihood for intrusions of CDW onto the continental shelf in this region. This suggests that during spring there are competing mechanisms of surface and basal melting of the Ross Ice Shelf, both of which are closely tied to natural tropical Pacific decadal variability. Moreover, that the projected transition of the IPO back to its positive phase in the coming decade, though likely to reduce surface warming on the Ross Ice Shelf, could increase the risk of disintegration of Ross Sea ice shelves due to increased intrusions of CDW and enhanced basal melting.

Lagrangian Analysis of Transport Pathways of Subtropical Water to the Primorye Coast

Lagrangian calculations based on satellite altimetry data (1993–2015) statistically demonstrated the existence of stable transport pathways of subtropical waters to the southern coasts of Russian Primorye through the subarctic front of the Sea of Japan. This transport is mainly provided by a peculiar mesoscale circulation north of the front as eddy streets, which facilitate the formation of Lagrangian intrusions of warm water penetrating further northward. The transport of warm waters in recent decades could be one of the factors responsible for the prolonged warm autumns observed in Primorye since the 1990s and explains the penetration of thermophilic fishes and other tropical and subtropical marine organisms and animals to the Primorye coasts.

Macronutrient and carbon supply, uptake and cycling across the Antarctic Peninsula shelf during summer.

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment.This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

Summer Drivers of Atmospheric Variability Affecting Ice Shelf Thinning in the Amundsen Sea Embayment, West Antarctica

AbstractSatellite data and a 35‐year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large‐scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves.

Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4

Abstract. An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of warm water from offshore.

Distribution of Different Biogeographical Tintinnids in Yellow Sea and Bohai Sea

There were different biogeographical tintinnids in the oceans. Knowledge of their distribution pattern and mixing was important to the understanding of ecosystem functions. Yellow Sea (YS) and Bohai Sea (BS) were semi-enclosed seas influenced by warm water intrusion and YS cold bottom water. The occurrence of tintinnids in YS and BS during two cruises (summer and winter) were investigated to find out: i) whether warm-water tintinnids appeared in YS and BS; ii) whether boreal tintinnids appeared in high summer; iii) the core area of neritic tintinnids and iv) how these different biogeographical tintinnids mixed. Our results showed that tintinnid community was dominated by neritic tintinnid. We confirmed the occurrence of warm-water tintinnids in summer and winter. In summer, they intruded into BS and mainly distributed in the upper 20 m where Yellow Sea Surface Warm Water (YSSWW) developed. In winter, they were limited in the surface water of central deep region (bottom depth > 50 m) of YS where were affected by Yellow Sea Warm Water (YSWW). Boreal tintinnids occurred in YS in high summer (August) and in winter, while they were not observed in BS. In summer, the highest abundance of boreal tintinnids occurred in Yellow Sea Bottom Cold Water, indicating the presence of an oversummering stock. In winter, they were concentrated in the north of YSWW. Vertically, neritic tintinnids abundance was high in the bottom layers. Horizontally, high neritic tintinnids abundance in bottom layers occurred along the 50 m isobath coinciding with the position of front systems. Front systems were the core distribution area of neritic tintinnids. High abundance areas of warm-water and boreal tintinnids were clearly separated vertically in summer, and horizontally in winter. High abundance of neritic tintinnids rarely overlapped with that of warm-water or boreal tintinnids.

Front‐Eddy Influence on Water Column Properties, Phytoplankton Community Structure, and Cross‐Shelf Exchange of Diatom Taxa in the Shelf‐Slope Area off Concepción (∼36–37°S)

AbstractIn eastern boundary current systems (EBCSs), submesoscale to mesocale variability contributes to cross‐shore exchanges of water properties, nutrients, and plankton. Data from a short‐term summer survey and satellite time series (January–February 2014) were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of Punta Lavapié, and to explore cross‐shelf exchanges of diatom taxa. A thermohaline front (FRN‐1) flanked by a mesoscale anticyclonic intrathermocline eddy (ITE‐1), or mode‐water eddy, persisted during the time series and the survey was undertaken during a wind relaxation event. At the survey time, ITE‐1 contributed to an onshore intrusion of warm oceanic waters (southern section) and an offshore advection of cold coastal waters (northern section), with the latter forming a cold, high chlorophyll‐a filament. In situ phytoplankton and diatom biomasses were highest at the surface in FRN‐1 and at the subsurface in ITE‐1, whereas values in the coastal zone were lower and dominated by smaller cells. Diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the FRN‐1 and ITE‐1 interaction area, suggesting that this mixture was the result of both offshore and onshore advection. Overall, front‐eddy interactions in EBCSs could enhance cross‐shelf exchanges of coastal and oceanic plankton, as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone, combined with ITE‐induced advection and vertical nutrient inputs to the surface layer.

Effects of increase glacier discharge on phytoplankton bloom dynamics and pelagic geochemistry in a high Arctic fjord

Arctic fjords experience extremely pronounced seasonal variability and spatial heterogeneity associated with changes in ice cover, glacial retreat and the intrusion of continental shelf’s adjacent water masses. Global warming intensifies natural environmental variability on these important systems, yet the regional and global effects of these processes are still poorly understood. In the present study, we examine seasonal and spatial variability in Kongsfjorden, on the western coast of Spitsbergen, Svalbard. We report hydrological, biological, and biogeochemical data collected during spring, summer, and fall 2012. Our results show a strong phytoplankton bloom with the highest chlorophyll a (Chla) levels ever reported in this area, peaking 15.5µg/L during late May and completely dominated by large diatoms at the inner fjord, that may sustain both pelagic and benthic production under weakly stratified conditions at the glacier front. A progressively stronger stratification of the water column during summer and fall was shaped by the intrusion of warm Atlantic water (T>3°C and Sal>34.65) into the fjord at around 100m depth, and by turbid freshwater plumes (T<1°C and Sal<34.65) at the surface due to glacier meltwater input. Biopolymeric carbon fractions and isotopic signatures of the particulate organic material (POM) revealed very fresh and labile material produced during the spring bloom (13C enriched, with values up to −22.7‰ at the highest Chl a peak, and high in carbohydrates and proteins content – up to 167 and 148µg/L, respectively-), and a clear and strong continental signature of the POM present during late summer and fall (13C depleted, with values averaging −26.5‰, and high in lipid content – up to 92µg/L-) when freshwater melting is accentuated. Our data evidence the importance of combining both physical (i.e. water mass dominance) and geochemical (i.e. characteristics of material released by glacier runoff) data in order to understand the timing, intensity and characteristics of the phytoplankton bloom in Kongsfjorden, a continuously changing system due to sustained warming. In a scenario where glacial retreat is predicted to increase the impacts of meltwater discharge and associated delivery of organic and inorganic material to the surrounding waters, special attention is required in order to predict the consequences for Arctic fjords and adjacent shelf ecosystems.

Responses of Basal Melting of Antarctic Ice Shelves to the Climatic Forcing of the Last Glacial Maximum and CO2 Doubling

Abstract Basal melting of the Antarctic ice shelves is an important factor in determining the stability of the Antarctic ice sheet. This study used the climatic outputs of an atmosphere–ocean general circulation model to force a circumpolar ocean model that resolves ice shelf cavity circulation to investigate the response of Antarctic ice shelf melting to different climatic conditions (i.e., to a doubling of CO2 and to the Last Glacial Maximum conditions). Sensitivity experiments were also conducted to investigate the roles of both surface atmospheric change and changes of oceanic lateral boundary conditions. It was found that the rate of change of basal melt due to climate warming is much greater (by an order of magnitude) than that due to cooling. This is mainly because the intrusion of warm water onto the continental shelves, linked to sea ice production and climate change, is crucial in determining the basal melt rate of many ice shelves. Sensitivity experiments showed that changes of atmospheric heat flux and ocean temperature are both important for warm and cold climates. The offshore wind change, together with atmospheric heat flux change, strongly affected the production of both sea ice and high-density water, preventing warmer water approaching the ice shelves under a colder climate. These results reflect the importance of both water mass formation in the Antarctic shelf seas and subsurface ocean temperature in understanding the long-term response to climate change of the melting of Antarctic ice shelves.

Пространственно-временные изменения видового состава и плотности популяций веслоногих ракообразных (Crustacea: Copepoda) в дальневосточном морском заповеднике ДВО РАН (Японское море)

Дальневосточный государственный морской заповедник ДВО РАН (ДВГМЗ) является самым богатым по разнообразию населения районом морей России, но сведений о пространственно-временной изменчивости зоопланктона в его акватории чрезвычайно мало, а последние наблюдения проводились более 20 лет назад. В данной работе приведены результаты современного исследования видового состава, плотности популяций и распределения веслоногих ракообразных — основных представителей зоопланктона в ДВГМЗ. Работа основана на сборах планктона, которые выполнялись ежемесячно на 10 станциях в акватории ДВГМЗ в пределах 50-метровой изобаты в июне — сентябре 2012 г. В этот сезон в заповеднике отмечается наибольшая изменчивость температуры воды. Обнаружен 21 вид копепод из двух отрядов (Calanoida — 17 видов и Cyclopoida — 4 вида). Наибольшее видовое богатство отмечено для родов Acartia и Oithona (по 4 вида). Преобладали морские виды — 80 % общего числа видов в пробах, а по отношению к биотопу — неритические (58 %). Широкобореальные виды составляли 55 % общего числа, тропические и субтропические — 45. Наибольшее количество видов копепод (16) отмечено в июне, наименьшее (5) — в сентябре. В июне — июле доминировали Oithona similis и Pseudocalanus newmani, в августе — Paracalanus parvus, Oithona brevicornis и Oithona similis, в сентябре — Paracalanus parvus и Oithona brevicornis. С июня по сентябрь происходило постепенное снижение обилия и разнообразия копепод во всех районах заповедника. Средняя плотность популяций копепод была максимальной в июне, в период развития холодноводных видов Oithona similis, Pseudocalanus newmani, Acartia hudsonica и Eurytemora pacifica, а минимальной — в сентябре. Наибольшие концентрации копепод отмечены в июне в западном районе заповедника в зал. Посьета (Посьетский рейд) над горизонтом глубины не более 10 м. По результатам кластерного анализа станций на акватории ДВГМЗ на основе коэффициента видового сходства Брэя — Кёртиса на уровне сходства 60 % выделены три комплекса планктонных копепод, видовой состав которых формируется под влиянием различных водных масс. Наибольшее видовое богатство и плотность копепод отмечены в комплексах западного и восточного районов заповедника. В мелководном комплексе западного района высокая плотность видов солоноватоводных родов Acartia, Eurytemora, Centropages, Tortanus и Pseudodiaptomus свидетельствует о присутствии там эстуарных и прибрежных вод. Наличие тропических и субтропических видов копепод (O. nana, Mesocalanus tenuicornis, Pseudodiatomus inopinus) подтверждает возможность проникновения в западный район тёплых вод из области Восточно-Корейского течения. В глубоководном комплексе восточного района совместное присутствие летом холодноводных и тепловодных видов копепод указывает на выраженную стратификацию водной толщи, где на глубине влияние оказывала холодная глубинная водная масса из Японского моря, а в верхнем слое — её более тёплая поверхностная модификация. В комплексе южного района заповедника, где доминировали панталассные и неритические виды, отмечены минимальные показатели видового богатства и плотности копепод. Обилие летом в этом комплексе холодноводных O. similis и P. newmani свидетельствует о поступлении холодных вод в придонный слой, а показатели численности копепод могут характеризовать степень влияния холодных вод на южную часть акватории заповедника. Особенности распределения копепод, их стабильно низкие показатели обилия и разнообразия в исследованной акватории к югу от ДВГМЗ могут быть вызваны опресняющим воздействием речных вод и возможным негативным влиянием загрязняющих веществ. Видовой состав и количественные характеристики копепод возможно использовать для оценки экологического состояния акватории морского заповедника.