Adjacent Ocean Research Articles

The transport and fate of marine plastics in South Africa and adjacent oceans

South Africa is thought to be one of the worst contributors of plastic into the sea globally. Although some plastic items derive from offshore sources (mainly fishing and other maritime activities, but also long-distance transport), the importance of local, land-based sources is indicated by the composition of beach debris and the concentration of macro-, meso- and microplastics close to urban source areas. Some 60–90% of plastic from land-based sources is expected to strand on beaches, but plastic standing stocks on beaches are much lower than global model predictions of land-based pollution. Burial in beaches and transport into backshore vegetation are significant sinks, although this plastic is likely to be released as the climate crisis leads to rising sea levels and more extreme storms. Most buried items are fairly small, while many larger items, which account for most of the mass of plastic, are removed from beaches by cleaning efforts. However, even daily accumulation rate estimates – which exclude the effects of cleaning – fall well short of model predictions of plastic leakage from land-based sources. Oceanographic models predict that plastics entering the sea from South Africa are exported to the South Atlantic and Indian Oceans, with the proportion depending on source location and item density. At sea, floating macroplastic is concentrated close to urban centres. Farther offshore, plastic items tend to be large and buoyant because biofouling causes small, low buoyancy items to sink. Size-selective removal of plastics by biota might also contribute to the paucity of floating microplastics (<1 mm). The seabed is likely to be the main long-term sink for waste plastics, but the limited data available indicate low levels of plastics on the seabed off South Africa. Only a small proportion of plastic predicted to leak into the sea from South Africa can be accounted for. However, this should not delay the implementation of effective mitigation measures to limit plastic leakage.
 Significance:
 
 High densities of waste plastic around urban centres indicate that most macro- and microplastics come from local, land-based sources and do not disperse far at sea.
 Beach clean-ups remove up to 90% of the mass of stranded plastic, largely found in macroplastic items (>25 mm).
 The seabed is a long-term sink for marine plastics, but densities of plastic on the seabed around South Africa are still modest.
 The global model prediction of plastic leakage from South Africa into the sea probably is a gross overestimate.

The roles of vegetation, tide and sediment in the variability of carbon in the salt marsh dominated tidal creeks

Combined effects of vegetation, tide and sediment on the carbon dynamics in the intertidal creek-marsh systems remain unclear. We investigated the variability of dissolved organic (DOC) and inorganic carbon (DIC), and particulate organic (POC) and inorganic carbon (PIC) in the tidal creeks within the Poaceae and Cyperaceae communities on flood-ebb cycle in a salt marsh of eastern China. In the Poaceae creek with high plant biomass and soil carbon stock, the DOC concentrations were higher by on average 1.00–1.48 times than that in the Cyperaceae creek across all seasons and spring and neap tide stages, while the difference of DIC was not notable. The POC and PIC concentrations were lower in the Poaceae creek compared to the Cyperaceae creek. Spring tides increased the carbon concentrations (except for PIC) in both creeks by on average 7–40%, relative to neap tides. Seasonal variations of sedimentary rate within the communities probably result in the discrepancy of particulate carbon loading between the creeks. The Poaceae creek functioned as a source of DOC and DIC throughout a year but as a sink of POC and PIC in summer and autumn, while it turned to a weak source of PIC in winter and spring. The Cyperaceae creek exhibited as a source of all carbon components throughout a year. We suggest that vegetation type (with soil carbon stocks), tidal regimes and sedimentary dynamics would synergistically determine the fate of carbon in the creeks. Our results are helpful in reliable estimates of carbon transport between the coastal marsh and the adjacent ocean.

Estimates of suspended solid transport in the Pará River Estuary

Abstract The aim of the present study was to quantify the suspended solid concentrations (CSSL) and suspended solid transport (TSSL) in the mixing zone of the Para River Estuary. This estuary is located at the southeastern extreme of the estuarine complex of the Amazon River, and receives input from Tocantins and Para rivers and other local tributaries, with a total discharge of approximately 104 m3 s-1. Two field campaigns were conducted to collect samples of Suspended Particulate Matter (SPM) and measure turbidity. Bottom and surface samples were collected hourly throughout a semidiurnal tidal cycle at two points in the estuary (Left Margin [LM]: -0.7287° -48.2408° and Right Margin [RM]: -0.6051° -48.4048°) in both the dry and rainy seasons. The TSSL was determined using a linear correlation between SPM and turbidity. The results indicate that both the RM and LM points were export routes of suspended solids to the adjacent ocean. However, both lateral and seasonal differences were observed in the PRE samples, with the RM point exporting more suspended solids to the adjacent ocean than the LM point. The TSSL was higher in near-bottom layers on the RM, and the lutocline was broader in comparison with the LM. The correlation between the CSSL at the bottom and in the water column was higher on the LM, and indicated that approximately 80% of the CSSL on this margin derives from resuspension. The sum of the evidence indicates that both points export suspended solids to the ocean.

Targeted Observations for Improving Prediction of the NAO Onset

Based on the viewpoint that the North Atlantic Oscillation (NAO) has an intrinsic timescale of approximate two weeks and can be treated as an initial value problem, targeted observations for improving the prediction of the onset of NAO events are investigated by using the conditional nonlinear optimal perturbation (CNOP) method with a quasi-geostrophic model. The results show that flow-dependent sensitive areas for the prediction of NAO onset are mainly located over North Atlantic and its upstream regions. Targeted observations over the main sensitive areas could improve NAO onset prediction in most cases (approximately 75%) due to reduced errors in anomalous eddy vorticity forcing (EVF) projection in the typical NAO mode. Moreover, a flow-independent sensitive area is determined based on the winter climatological flow, which is located over North America and its adjacent ocean. The NAO onset prediction can also be improved by targeted observations over the flow-independent sensitive area, but the skill improvement is somewhat lower than that derived from observations over the flow-dependent sensitive area. The above results indicate that targeted observations over sensitive areas identified by the CNOP method can help to improve the onset prediction of NAO events.

Gelo Marinho Antártico e a Trajetória de Ciclones sobre o Oceano Atlântico do Sul

Os ciclones desempenham um papel importante na circulação geral da atmosfera, possibilitando os transportes meridionais de calor, umidade e momento excedentes das baixas latitudes para altas latitudes. No Atlântico Sul as áreas mais favoráveis para a formação de ciclones são próximo à costa leste da América do Sul (30°S a 45°S) e Península Antártica. Um dos fatores que favorecem a formação da ciclogênese na costa leste da América do Sul é o contraste de temperatura entre o oceano Atlântico Sul com a camada de ar superficial. Enquanto que a ciclogênese próxima à Península Antártica pode estar associada a instabilidades baroclínicas pré existentes em níveis mais altos da atmosfera. O objetivo deste trabalho é investigar qual o papel da Península Antártica no comportamento dos ciclones extratropicais que atuam sobre a América do sul e oceanos adjacentes. Para tal, foi aplicado o algoritmo TRACK para rastreamento dos ciclones. A interação oceano-atmosfera será investigada por meio do modo oceano-atmosfera do modelo acoplado COAWST. A execução do TRACK se mostrou satisfatória, uma vez que os resultados encontrados corroboram com a literatura da região.

Advances in research of the mid-deep South China Sea circulation

The South China Sea (SCS) is a large marginal sea connecting the Indian and Pacific oceans. Under the factors of monsoons, strait transport, and varied bathymetry, the SCS presents a three-layer structure and strong diapycnal mixing which is far greater than that in the open ocean. Theoretical analysis and observations reveal that internal tides, internal solitary waves, and strong winds are the sources of the strong mixing in the northern SCS. A major consequence of the strong mixing is an active mid-deep circulation system. This system promotes exchange of water between the SCS and adjacent oceans, and also regulates the upper layer of wind-driven circulation, making the 3 dimensional SCS circulation clearly different from that in other tropical and subtropical marginal seas. The mass transport capacity of the mid-deep circulation has a substantial impact on marine sedimentation, the biogeochemical cycle, and other processes in the SCS. This paper summarizes the recent advances in mid-deep sea circulation dynamics of the SCS, and discusses the opportunities and challenges in this area.

Mean sea surface model over China seas and its adjacent ocean established with the 19-year moving average method from multi-satellite altimeter data

A new mean sea surface (MSS) model (named Shandong University of Science and Technology (2018) (SUST2018) MSS model) with a grid of 1′ × 1′ over China seas and its adjacent ocean (0°N~41°N, 100°E~140°E) is established and validated. The SUST2018 model established with the 19-year moving average method is based on 26-year multi-satellite altimeter data covering the time period 1992–2018. The new altimetry data of HaiYang-2A (HY-2A), Jason-3 and Sentinel-3A have been used in establishing the SUST2018 model. The process of the establishment of the MSS model also have been presented, including collinear adjustment of exact repeat mission (ERM) data, removal of the temporal oceanic variability of geodetic mission (GM) data, crossover adjustment and gridding. The reliability and accuracy of SUST2018 are validated by comparing with the CLS15 and DTU18 MSS models as well as satellite altimeter data. By comparing SUST2018 and SUST(all)2018 (established with the traditional average method), it can be found that the accuracy of SUST2018 is higher than that of SUST(all)2018, which indicates that the 19-year moving average method can effectively improve the accuracy of an MSS model.

Temperature, Wind, Cloud, and the Postglacial Tree Line History of Sub-Antarctic Campbell Island

Campbell Island, which is 600 km south of New Zealand, has the southernmost tree line in this ocean sector. Directly under the maximum of the westerlies, the island is sensitive to changes in wind strength and direction. Pollen records from three peat cores spanning the tree line ecotone provide a 17,000-year history of vegetation change, temperature, and site moisture. With postglacial warming, tundra was replaced by tussock grassland 12,500 years ago. A subsequent increase of shrubland was reversed at 10,500 years ago and wetland-grassland communities became dominant. Around 9000 years ago, trees spread, with maximum tree line elevation reached around 6500 to 3000 years ago. This sequence is out of step with Southern Ocean sea surface temperatures, which were warmer than 12,500 to 9000 years ago, and, subsequently, cooled. Campbell Island tree lines were decoupled from temperature trends in the adjacent ocean by weaker westerlies from 12,500 to 9000 years ago, which leads to the intrusion of warmer, cloudier northern airmasses. This reduced solar radiation and evapotranspiration while increasing atmospheric humidity and substrate wetness, which suppressed tree growth. Cooler, stronger westerlies in the Holocene brought clearer skies, drier air, increased evapotranspiration, and rising tree lines. Future global warming will not necessarily lead to rising tree lines in oceanic regions.

A 68 ka precipitation record from the hyperarid core of the Atacama Desert in northern Chile

Abstract The Atacama Desert in northern Chile is one of the driest deserts on Earth. Hyperaridity persists at least since the Miocene and was punctuated by pluvial phases. However, very little is known about the timing, regional spread and intensities of precipitation changes. Here, we present a new precipitation record from a sedimentary sequence recovered in a tectonically blocked endorheic basin that is located in the hyperarid core of the Atacama Desert. The chronostratigraphic framework of the record is given by a multi-disciplinary dating approach, suggesting an age of ca. 68 ka BP for the core base. The sequence consists of three sediment types, whose sedimentological and geochemical characteristics suggest different depositional processes that reflect different degrees in humidity. First, particularly fine-grained sediments with high clastic but low calcium sulfate and carbonate contents reflect a particularly dry climate with only sporadic precipitation events and fluvial supply via channel systems. Second, more coarse-grained sediments with lower clastic and higher calcium sulfate and carbonate contents reflect more moist conditions with stronger precipitation events that lead to fluvial activity not restricted to the channels but involving the slopes and plains in the catchment. Third, normally graded layers with an equally high proportion of calcium sulfate and carbonate reflect occasional high-precipitation events that caused sediment supply also from most distant parts of the catchment via severe flash floods. The sedimentary succession suggests that precipitation changes took place on orbital but also on millennial time scales. Rather moist periods occurred during most of MIS 2, several shorter periods within MIS 3 and parts of MIS 4. Comparison of the findings from the Huara record with selected climate records from continental and marine sites in South America suggests a strong precipitation heterogeneity across the Atacama. This heterogeneity is caused by pronounced differences in the dominating climate patterns and a shift from predominant summer rain in the north to winter rain in the south. Precipitation supply to the Huara clay plan is controlled by the atmospheric circulation rather than the surface temperature of the adjacent ocean.

Possible Impacts of Snow Darkening Effects on the Hydrological Cycle over Western Eurasia and East Asia

In this paper, we investigated the possible impact of snow darkening effect (SDE) by light-absorbing aerosols on the regional changes of the hydrological cycle over Eurasia using the NASA GEOS-5 Model with aerosol tracers and a state-of-the-art snow darkening module, the Goddard SnoW Impurity Module (GOSWIM) for the land surface. Two sets of ten-member ensemble experiments for 10 years were carried out forced by prescribed sea surface temperature (2002–2011) with different atmospheric initial conditions, with and without SDE, respectively. Results show that SDE can exert a significant regional influence in partitioning the contributions of evaporative and advective processes on the hydrological cycle, during spring and summer season. Over western Eurasia, SDE-induced rainfall increase during early spring can be largely explained by the increased evaporation from snowmelt. Rainfall, however, decreases in early summer due to the reduced evaporation as well as moisture divergence and atmospheric subsidence associated with the development of an anomalous mid- to upper-tropospheric anticyclonic circulation. On the other hand, in the East Asian monsoon region, moisture advection from the adjacent ocean is a main contributor to rainfall increase in the melting season. A warmer land-surface caused by earlier snowmelt and subsequent drying further increases moisture transport and convergence significantly enhancing rainfall over the region. Our findings suggest that the SDE may play an important role in leading to hotter and drier summers over western Eurasia, through coupled land-atmosphere interaction, while enhancing East Asian summer monsoonal precipitation via enhanced land-ocean thermal contrast and moisture transport due to the SDE-induced warmer Eurasian continent.

Temporal variability of the mass exchanges between the main inlet of Ria Formosa lagoon (southwestern Iberia) and the Atlantic Ocean

Understanding the mass exchange patterns between coastal lagoons and ocean plays a key role to explain their impact upon the water quality and biological productivity of these systems. Ria Formosa is a temperate lagoon on the southwestern coast of Iberia, one of the most important coastal system in this region in terms of biological productivity, ecological and economic values. Given its relevance and strong interconnectivity with the adjoining ocean, the quantification of these exchanges is a key issue that had not yet been thoroughly addressed. In this context, this study is focused on understanding the role of Ria Formosa's main inlet in terms of mass budgets dynamics of water, nutrients, suspended solids and chlorophyll a with the Atlantic Ocean and to identify its seasonal variability. In order to attain this purpose, the influence of the forcing mechanisms at different time scales, including tides, oceanographic/meteorological synoptic conditions and seasons, was assessed. To accomplish this, six semidiurnal tidal cycles surveys were conducted at Faro-Olhão inlet, comprising hourly water samples collection and in situ measurements at a selected cross-section of the inlet channel. Results revealed that mass exchanges variability through Faro-Olhão inlet was mainly due to oceanographic processes (upwelling and coastal countercurrent events) and, secondly, to phytoplankton activity within the lagoon. Seasonally, regardless the direction of the residual current through the inlet, Ria Formosa acted as a source of material during Spring and Summer seasons, which contributed to increase the biological productivity of the coastal ocean. Upwelling events that occurred more evidently during the Autumn survey drove an import amount of nutrients into the lagoon, enhancing its biological productivity. Furthermore, the rainfall period that prevailed before the Winter survey contributed to export material and nutrients to the adjacent ocean, confirming that Ria Formosa fertilizes the coastal ocean, even during a period of low productivity.

Seasonal and inter-annual variability of net primary production in the NW Iberian margin (1998–2016) in relation to wind stress and sea surface temperature

Seasonal and inter-annual variability of satellite-derived net primary production (NPP) in the NW Iberian margin and its relationship with the offshore Ekman transport (-Qx) and a variety of sea surface temperature (SST) indices have been examined over the period 1998–2016. Seasonality explained about 55% of NPP variability over the shelf and the adjacent ocean. Maximum NPP rates occurred by May in the adjacent ocean, and were delayed until July over the shelf. The excess production (ΔNPP) over the shelf compared to the ocean domain represented 0.45 ± 0.02 g C m−2 d−1 or 37 ± 2% of the total NPP and peaked in August, in between the maximum -Qx and the maximum SST difference between the shelf and the adjacent ocean (ΔSST). During the upwelling season, the inter-annual variability of NPP in the adjacent ocean correlated positively with the spring stratification (SSTstr) and the average -Qx over the upwelling season and ΔNPP correlated inversely with ΔSST. Conversely, during the downwelling season, ΔNPP correlated with the average stratification (SSTdown) over the downwelling season. The rates of change of NPP with the climate-related variables (-Qx, ΔSST, SSTstr, SSTdown), obtained from these regressions, may be used to test the sensitivity of the NW Iberian upwelling productivity to climate change.

Is positive correlation between cloud droplet effective radius and aerosol optical depth over land due to retrieval artifacts or real physical processes?

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3, Clouds and the Earth's Radiant Energy System (CERES) Edition-4 L3 products, and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data are employed to systematically study aerosol–cloud correlations over three anthropogenic aerosol regions and their adjacent oceans, as well as explore the effect of retrieval artifacts and underlying physical mechanisms. This study is confined to warm phase and single-layer clouds without precipitation during the summertime (June, July, and August). Our analysis suggests that cloud effective radius (CER) is positively correlated with aerosol optical depth (AOD) over land (positive slopes), but negatively correlated with aerosol index (AI) over oceans (negative slopes) even with small ranges of liquid water path (quasi-constant). The changes in albedo at the top of the atmosphere (TOA) corresponding to aerosol-induced changes in CER also lend credence to the authenticity of this opposite aerosol–cloud correlation between land and ocean. It is noted that potential artifacts, such as the retrieval biases of both cloud (partially cloudy and 3-D-shaped clouds) and aerosol, can result in a serious overestimation of the slope of CER–AOD/AI. Our results show that collision–coalescence seems not to be the dominant cause for positive slope over land, but the increased CER caused by increased aerosol might further increase CER by initializing collision–coalescence, generating a positive feedback. By stratifying data according to the lower tropospheric stability and relative humidity near cloud top, it is found that the positive correlations more likely occur in the case of drier cloud top and stronger turbulence in clouds, while negative correlations occur in the case of moister cloud top and weaker turbulence in clouds, which implies entrainment mixing might be a possible physical interpretation for such a positive CER–AOD slope.

Common cause for severe droughts in South America and marine heatwaves in the South Atlantic

In 2013/14 eastern South America experienced one of its worst droughts. At the same time an unprecedented marine heatwave developed in the western South Atlantic. The drought was linked to suppression of the South Atlantic convergence zone and its associated rainfall, which led to water shortages in Brazil and impacted food supplies globally. Here we show from observations that such droughts and adjacent marine heatwaves have a common remote cause. Atmospheric blocking triggered by tropical convection in the Indian and Pacific oceans can cause persistent anticyclonic circulation that not only leads to severe drought but also generates marine heatwaves in the adjacent ocean. We show that increased shortwave radiation due to reduced cloud cover and reduced ocean heat loss from weaker winds are the main contributors to the establishment of marine heatwaves in the region. The proposed mechanism, which involves droughts, extreme air temperature over land and atmospheric blocking explains approximately 60% of the marine heatwave events in the western South Atlantic. We also identified an increase in frequency, duration, intensity and extension of marine heatwave events over the satellite period 1982–2016. Moreover, surface primary production was reduced during these events with implications for regional fisheries. Droughts in South America and marine heatwaves in the South Atlantic have a common remote cause, convection in the tropical oceans that triggers atmospheric blocking, suggest analyses of observations.

A Deficit of Seasonal Temperature Forecast Skill over West Coast Regions in NMME

Abstract This study investigates the forecast skill of seasonal-mean near-surface (2 m) air temperature in the North American Multimodel Ensemble (NMME) Phase 2, with a focus on the West Coast of the United States. Overall, 1-month lead time NMME forecasts exhibit skill superior or similar to persistence forecasts over many continental regions, and skill is generally higher over the ocean than the continent. However, forecast skill along most West Coast regions is markedly lower than in the adjacent ocean and interior, especially during the warm seasons. Results indicate that the poor forecast skill along the West Coast of the United States reflects deficiencies in their representation of multiple relevant physical processes. Analyses focusing on California find that summer forecast errors are spatially coherent over the coastal region and the inland region individually, but the correlation of forecast errors between the two regions is low. Variation in forecast performance over the coastal California region is associated with anomalous geopotential height over the lower middle latitudes and subtropics of the eastern Pacific, North America, and the western Atlantic. In contrast, variation in forecast performance over the inland California region is associated with the atmospheric circulation over the western United States. Further, it is found that forecast errors along the California coast are linked to anomalies of low cloudiness (stratus clouds) along the coastal region.

Dynamic characterization of the main Cantabrian river plumes by means of MODIS

River plumes formed in the Cantabrian coast of the Bay of Biscay constitute the main source of nutrients for this coastal area. They are able to sustain high levels of phytoplankton and primary productivity which, in turn, affect the associated ecosystems. Moreover, these plumes also influence other processes as stratification, flow circulation, transport of pollutants or erosion-sedimentation patterns, affecting the morphodynamical and biogeochemical characteristics of the area, which makes their study of high importance. The general small extension of these plumes makes necessary the use of high spatial and temporal resolution data to characterize their fine-spatial structure and to identify their evolution that happens at a short time scale. For that, the response of the Cantabrian plumes to the main forcing was analyzed by means of data provided by the Moderate Resolution Imaging Spectroradiometer sensor onboard Aqua and Terra satellites, which provides daily high resolution of up to 250 m. Composite images of Nalon, Pas-Besaya, Nervion and Adour plumes were created to analyze the effect of each forcing, including river discharge, wind and tides.Adour is the only Cantabrian plume formed even under low discharges due to the greater basin and river discharge. The rest of Cantabrian plumes are only well developed under high river discharges, which shows this forcing as the most important. Nalon, Pas-Besaya and Nervion plumes mainly influence eastward locations whereas Adour plume mainly affects areas located north of river mouth, due to the predominant currents in each area. Wind has a remarkable impact when plumes are well developed, being especially important in Nalon, Pas-Besaya and Nervion plumes. Plume material is dispersed to the ocean (under upwelling and seaward winds) or retained near coast (under downwelling and landward winds) attending to the main wind direction, conditioning the characteristics of the plume area. The semidiurnal tidal cycle is also important when plumes are developed, being all of them greater under low tidal conditions, although the impact is less important in the Adour plume. The higher stability of Adour plume to the forcing could be related to the much greater extension, which makes necessary stronger forcing to cause similar effects. On the other hand, this greater extension favors its impact on thermohaline properties of seawater. The Adour River is able to provoke winter stratification in the plume area, as well as thermal inversions, which condition the thermohaline properties respect to oceanic area not affected by the plume.By last, the influence of Cantabrian plumes on the annual cycle of chlorophyll was evaluated for each plume area and the adjacent ocean also by means of MODIS data. A chlorophyll peak was detected in both areas for early spring and high values of chlorophyll were also detected during autumn and winter but only in plume areas, associated to the input of nutrients and the haline stratification promoted by the high rivers discharges during these months.

Endemicity and Community Composition of Marine Species along the NW Pacific and Adjacent Arctic Ocean

The Northwestern (NW) Pacific Ocean lies in one of the most productive, speciose, and diverse regions of the World Ocean, and includes several shallow-water oceanic islands and deep-sea basins of varying depth, hydrology, and degree of isolation. The adjacent Arctic Ocean areas include the northern Bering and southern Chukchi Seas of the Arctic Ocean with short food chains and shallow depths characterizing high productivity areas. Despite its magnitude and relevance, characterization of species diversity and community composition patterns in the NW Pacific Ocean remains poorly explored and largely unknown. Here we attempt to discover how geographic boundaries and depth shape current community assemblages and delimit species distribution ranges and richness using open access data. We also show how endemicity and community composition vary between tropical and temperate NW Pacific and the adjacent Arctic Ocean considering sampling bias. The Eastern Philippine Sea was the hotspot of species richness in the NW Pacific and its adjacent Arctic Ocean even when accounting for sampling bias. The lowest species richness was observed in Papau. Despite high species richness in the Eastern Philippine Sea, the Yellow Sea and Gulf of Tonkin had the highest endemicity rates (ca. 60%) among all other ecoregions. Endemicity ranged 20–40% across 19 ecoregions. Chordata, Arthropoda, and Mollusca contributed more than 50% to the total community composition in the NW Pacific where as Arthropoda, Annelida, and Mollusca were the dominant taxa shaping ca. 82% of the Arctic Ocean community. Pelagic species richness was higher than the benthic one in both shallow-water and deep-sea regions of the NW Pacific Ocean. However, in the shallow and deep Arctic Ocean, most of the taxa were benthic excluding the deep Kara Sea where pelagic deep-sea species dominated the whole community. Two significantly distinctive clusters (North and South clusters) were classified based on species richness similarity analysis in this area including ecoregions of the (1) Arctic Ocean and North NW Pacific, and (2) Mid to South NW Pacific.

El Niño–Like Physical and Biogeochemical Ocean Response to Tropical Eruptions

AbstractThe oceanic response to recent tropical eruptions is examined in Large Ensemble (LE) experiments from two fully coupled global climate models, the Community Earth System Model (CESM) and the Geophysical Fluid Dynamics Laboratory Earth System Model (ESM2M), each forced by a distinct volcanic forcing dataset. Following the simulated eruptions of Agung, El Chichón, and Pinatubo, the ocean loses heat and gains oxygen and carbon, in general agreement with available observations. In both models, substantial global surface cooling is accompanied by El Niño–like equatorial Pacific surface warming a year after the volcanic forcing peaks. A mechanistic analysis of the CESM and ESM2M responses to Pinatubo identifies remote wind forcing from the western Pacific as a major driver of this El Niño–like response. Following eruption, faster cooling over the Maritime Continent than adjacent oceans suppresses convection and leads to persistent westerly wind anomalies over the western tropical Pacific. These wind anomalies excite equatorial downwelling Kelvin waves and the upwelling of warm subsurface anomalies in the eastern Pacific, promoting the development of El Niño conditions through Bjerknes feedbacks a year after eruption. This El Niño–like response drives further ocean heat loss through enhanced equatorial cloud albedo, and dominates global carbon uptake as upwelling of carbon-rich waters is suppressed in the tropical Pacific. Oxygen uptake occurs primarily at high latitudes, where surface cooling intensifies the ventilation of subtropical thermocline waters. These volcanically forced ocean responses are large enough to contribute to the observed decadal variability in oceanic heat, carbon, and oxygen.

Analysis of Severe Droughts in Taiwan and its Related Atmospheric and Oceanic Environments

Drought is one of the important issues in climate studies. A drought index, Taiwan Meteorological Drought index (TMD index), was previously proposed and is applied here to identify historical severe droughts in Taiwan in order to clarify the corresponding large-scale backgrounds as a potential alert to the society in future. Through the TMD index, several historical severe drought cases in Taiwan are detected and characterized by significant seasonal variability in the annual cycle. Composites for large-scale atmospheric and oceanic environments over different periods within the dry season are conducted. From October to December, the colder sea surface temperature (SST) pattern of Pacific Meridional Mode (PMM) and the PMM-induced local anomalous anticyclones over the South China Sea are both in charge of the extremely dry conditions in Taiwan. From January to February, cold SST in the South China Sea and its adjacent oceans dominates local atmospheric conditions above these regions and creates an unfavorable environment for convection systems. From March to May, a massive anomalous anticyclonic circulation centering beside Alaska and extending its properties to East Asia and Taiwan generates a descending environment and in turn suppresses convection systems to develop. Therefore, the extremely dry conditions under this system are expected.

Impacts of recent decadal changes in Asian aerosols on the East Asian summer monsoon: roles of aerosol\u2013radiation and aerosol\u2013cloud interactions

Anthropogenic aerosols (AA) can affect cloud and precipitation through aerosol–radiation interaction (ARI) and aerosol–cloud interaction (ACI). Over the past few decades, anthropogenic aerosol emissions have exhibited remarkable changes in the magnitude and in spatial pattern. The most significant changes are the increased emissions over both South Asia and East Asia. In this study, the atmospheric component of a state-of-the-art climate model that includes eight species of tropospheric aerosols, coupled to a multi-level mixed-layer ocean model, has been used to investigate the impacts of Asian anthropogenic aerosol precursor emission changes from 1970s to 2000s on large scale circulation and precipitation in boreal summer over East Asia. Results reveal significant changes in circulation and clouds over East Asia and over the tropical and western North Pacific (WNP). Increased Asian AA emissions lead to anomalous cyclonic circulation over the Maritime continent (MC) and anomalous anticyclonic circulation over the WNP, resulting in anomalous moisture transport convergence over the MC and therefore increased precipitation. They also lead to anomalous moisture flux divergence over both the WNP and large land areas of East Asia, especially over northern China, and therefore decreased precipitation there. These large scale circulation anomalies over the adjacent oceans are related to aerosol change induced ocean feedbacks, predominantly through ACI. It is the slow responses over the adjacent oceans (e.g., SST changes) through coupled atmosphere–ocean interaction in pre-monsoon seasons and summer that shape the changes of the East Asian summer monsoon and local precipitation. The results in this study suggest that increased Asian AA emissions from 1970s to 2000s may have played an important role for the observed southward shift of the Pacific intertropical convergence zone and precipitation belt, weakening of East Asian summer monsoon and reduced precipitation over northern China in East Asia during the latter half of the twentieth century.