Impact of transparent exopolymer particles on the dynamics of dissolved organic carbon in the Amundsen Sea,Antarctica

The Southern Ocean is an important carbon sink pool and plays a critical role in the global carbon cycling.The Amundsen Sea was reported to be highly productive in inshore area in the Southern Ocean.In order to investigate the influence of transparent exopolymer particles(TEP)on the behavior of dissolved organic carbon(DOC)in this region,a comprehensive study was conducted,encompassing both open water areas and highly productive polynyas.It was found that microbial heterotrophic metabolism is the primary process responsible for the production of humic-like fluorescent components in the open ocean.The relationship between apparent oxygen utilization and the two humic-like components can be accurately described by a power-law function,with a conversion rate consistent with that observed globally.The presence of TEP was found to have little impact on this process.Additionally,the study revealed the accumulation of DOC at the sea surface in the Amundsen Sea Polynya,suggesting that TEP may play a critical role in this phenomenon.These findings contribute to a deeper understanding of the dynamics and surface accumulation of DOC in the Amundsen Sea Polynya,and provide valuable insights into the carbon cycle in this region.

Sources and transformations of nitrite in the Amundsen Sea in summer 2019 and 2020 as revealed by nitrogen and oxygen isotopes

In this study,the nitrogen and oxygen isotope compositions of nitrite in the upper 150 m water column of the Amundsen Sea in the summer of 2019 and 2020 were measured to reveal the distribution and transformation of nitrite in the euphotic zone of the Southern Ocean.We found that primary nitrite maxima(PNMs)are widely present in the Amundsen Sea,where the depth of occurrence deepens from east to west and nitrite concentrations increases.Evidence from dual isotopes suggests that the formation of PNMs in all regions of the Amundsen Sea is dominated by ammonia oxidation.More importantly,the nitrogen and oxygen isotope compositions of nitrite in the Amundsen Sea mixed layer are abnormal,and their depth profiles are mirror symmetrical.Isotopic anomalies exhibit spatial variations,with central surface water having the lowest nitrogen isotope composition(−89.9‰±0.2‰)and western surface water having the highest oxygen isotope composition(63.3‰±0.3‰).Isotopic exchange reaction between nitrate and nitrite is responsible for these isotope anomalies,as both nitrogen and oxygen isotopes have large isotopic fractionation and opposite enrichment effects.This proves that isotopic exchange reaction operates extensively in different regions of the Amundsen Sea.Our study highlights the unique role of dual isotopes of nitrite in deepening the understanding of nitrogen cycle.Further studies on ammonia oxidation and isotopic exchange between nitrate and nitrite are warranted in the future to understand their roles in the nitrogen cycle in the Southern Ocean.

Physical-chemical and biological control of the zooplankton community in the Amundsen Sea, Antarctica

Zooplankton are critical components of the Southern Ocean ecosystems,acting as trophic links between phytoplankton and higher-level species.The composition,abundance,carbon biomass,and community structure of zooplankton were studied based on samples collected with a Norpac net(330-μm mesh,0.5-m^(2) net mouth)during the austral summers of 2017/2018.Three communities in a latitudinal gradient were identified based on both a zooplankton abundance dataset and a biomass dataset.Zooplankton were mainly dominated by small copepods(e.g.,Oithona similis and Ctenocalanus citer)in terms of abundance,while the total zooplankton biomass was dominated by krill(Euphausia superba and Thysanoessa macrura)and large copepods(e.g.,Calanoides acutus,Calanus propinquus,and Metridia gerlachei).Redundancy analysis demonstrated that environmental factors(e.g.,temperature,nitrate,dissolved oxygen,ammonium)accounted for more than 40%of the variance in zooplankton abundance/biomass.This indicates that physical processes significantly affect the zooplankton community.Meanwhile,a significant positive correlation was found between the abundance/biomass of zooplankton and that of dominant phytoplankton and ciliates,which suggests trophic links among various plankton functional groups.Our results reveal that both physical processes and biological factors shape the community structure of zooplankton in the Amundsen Sea.

Distributions of dissolved oxygen and apparent oxygen utilization in the Cosmonaut Sea and Amundsen Sea in austral summer 2021

Dissolved oxygen(DO)and apparent oxygen utilization(AOU)are crucial parameters for investigating marine ecosystem evolution and the marine environment.In this study,DO and AOU data were obtained and their spatial distribution characteristics were explored in the Cosmonaut Sea and Amundsen Sea in austral summer 2021.The standard deviation range of DO parallel samples was<0.1–3.7μmol·L–1,which met the accuracy requirements of the survey method.The DO concentration decreased sharply with water depth in the photic zone and increased slowly to the bottom.AOU in the surface layer of the two seas was significantly negatively correlated with chlorophyll a(p<0.01),and AOU was significantly lower in the south Cosmonaut Sea than in the north Cosmonaut Sea and Amundsen Sea(p<0.01).In austral summer,AOU was as low as<130μmol·L–1 in the nearshore Cosmonaut Sea with thicker Antarctic Surface Water down to ca.500 m.In early winter,AOU was lower than 50μmol·L–1 in the north Amundsen Sea in subsurface water(75–150 m).The unmodified Circumpolar Deep Water with high AOU(>160μmol·L–1)could surge up to ca.150–200 m in both seas,with stronger intrusion in the Amundsen Sea.The AOU in bottom water was significantly lower(p<0.01)in the Cosmonaut Sea(118.9±11.8μmol·L–1)than the Amundsen Sea(141.7±7.4μmol·L–1),indicating the stable existence of fresh oxygen-rich Antarctic Bottom Water in the Cosmonaut Sea.

Changes in Tintinnid Assemblages from Subantarctic Zone to Antarctic Zone Along Transect in Amundsen Sea(West Antarctica) in Early Austral Autumn

Tintinnid ciliates are important pelagic microplankton.Most studies previously conducted in the Amundsen Sea have covered a relatively small latitude range and provided minimal information about tintinnid species composition and distribution.The present study was conducted to investigate tintinnid assemblages from the Antarctic zone(AZ)northward through the polar front(PF)to the subantarctic zone(SAZ).A total of 17 tintinnid species belonging to seven genera were collected,and 16 were identified.Results show that nine of the species are endemic to the Southern Ocean and they mainly inhabit the AZ near Antarctic continent with an abundant proportion exceeding 60%of total tintinnid.According to the tintinnid abundance distribution,the species were divided into four groups:Group I includes Acanthostomella norvegica,Codonellopsis glacialis,C.pusilla and Cymatocylis antarctica and mainly occurs in the northern boundary of the PF;Group II includes Cymatocylis convallaria forma calyciformis,an unidentified species,and Amphorellopsis quinquealata and mainly inhabits the PF;Group III includes Salpingella costata,Cymatocylis vanhoeffeni,C.convallaria forma cristallina,C.convallaria forma drygalskii,C.convallaria,Codonellopsis gaussi,and Laackmanniella naviculaefera and mainly occurs in the AZ near the Antarctic continent;and Group IV,which comprises Salpingella sp.and inhabits all zones.The new species of tintinnid(belonging to Group II)primarily inhabit the AZ but also are distributed in the PF,and they have large lorica-oral-diameter(LOD).The distribution ranges of tintinnid assemblages from the AZ to PF were determined,in addition to the different assemblages mixed in the PF.The information provided in this study increases our understanding of tintinnid assemblages from the Antarctic continent in the Antarctic Circumpolar Current and Antarctic waters.

The potential distribution of adult Antarctic krill in the Amundsen Sea

Antarctic krill is the key species of ecological system in the Amundsen Sea.At present,the suitable distribution is unobtainable by scientifi c surveys or data from the fi shery.In this paper,the maximum entropy algorithm(Maxent)was used to obtain the potential distribution of adult Antarctic krill in order to provide useful information and reasonable reference for the policy on protecting potential krill habitats around the Amundsen Sea.Occurrence points and 17 environmental variables were used to simulate the distributions.Results show that the high and moderate suitable habitats lie between 65°S and 72°S in the Amundsen Sea.The high suitable habitat accounts for 8.1%of the total area of the Amundsen Sea.The sea ice persistence(ICE),total phytoplankton(PHYC),and the minimum value of dissolved iron(Fe_min)are the three dominant contributors to the model.Results from the response curves show that Antarctic krill preferred habitats with ICE of 0.42-0.93,PHYC of 2.48-2.77 mmol/m^(3) and Fe_min of(7.10×10^(-5))-(9.45×10^(-5))mmol/m 3.Positive trends existed in the PHYC of the high and moderate suitable habitat,and a positive trend existed in the Fe_min of moderate suitable habitat.However,the probability of presence of Antarctic krill will decrease if the increase of the PHYC and Fe_min continues.

Towards More Snow Days in Summer since 2001 at the Great Wall Station,Antarctic Peninsula:The Role of the Amundsen Sea Low

The variation in the precipitation phase in polar regions represents an important indicator of climate change and variability.We studied the precipitation phase at the Great Wall Station and Antarctic Peninsula(AP)region,based on daily precipitation,synoptic records and ERA-Interim data during the austral summers of 1985?2014.Overall,there was no trend in the total precipitation amount or days,but the phase of summer precipitation(rainfall days versus snowfall days)showed opposite trends before and after 2001 at the AP.The total summer rain days/snow days increased/decreased during 1985?2001 and significantly decreased at a rate of?14.13 d(10 yr)?1/increased at a rate of 14.31 d(10 yr)?1 during 2001?2014,agreeing well with corresponding variations in the surface air temperature.Further,we found that the longitudinal location of the Amundsen Sea low(ASL)should account for the change in the precipitation phase since 2001,as it has shown a westward drift after 2001[?41.1°(10 yr)?1],leading to stronger cold southerly winds,colder water vapor flux,and more snow over the AP region during summertime.This study points out a supplementary factor for the climate variation on the AP.

Contraction and warming of Antarctic Bottom Water in the Amundsen Sea

Antarctic Bottom Water(AABW)plays an important role in the meridional overturning circulation and contributes significantly to global heat transport and sea level rise(SLR).Based on the Global Ocean(1/12)°Physical Reanalysis(GLORYS12V1)products and conductivity-temperature-depth instrument data from the World Ocean Circulation Experiment hydrographic program,we analyzed the trends in the thickness,volume,temperature,salinity,and neutral density of the AABW in the Amundsen Sea from 1993 to 2017.Over the past 25 years,the volume has decreased by 3.45×10^(12) m^(3)/a,thinning at a rate of 5 m/a.In the vertical direction,the contraction of the AABW is compensated by the volume expansion of the Circumpolar Deep Water.As the volume of AABW decreases,the temperature of the AABW increases by about 0.002℃/a.This warming is equivalent to a heat flux of 0.27 W/m^(2).A local SLR is produced due to thermal expansion of 0.35 mm/a.During the study period,the neutral density decreased by 0.0003 kg/(m^(3)·a)due to warming.In the horizontal direction,the volume of AABW flowing from the Ross Sea into the Amundsen Sea gradually decreases and the temperature of the AABW increases continuously.The horizontal transport loss of the AABW volume is 4.07×10^(14) m^(3) and the horizontal heat transport results in a 0.03℃ increase in the temperature of the AABW.

Characteristics of hydrogen/oxygen isotopes in water masses and implications for spatial distribution of freshwater in the Amundsen Sea,Southern Ocean

Antarctica’s marginal seas are of great importance to atmosphere-ocean-ice interactions and are sensitive to global climate change.Multiple factors account for the freshwater budget in these regions,including glacier melting,seasonal formation/decay of sea ice,and precipitation.Hydrogen(H)and oxygen(O)isotopes represent useful proxies for determining the distribution and migration of water masses.We analyzed the H and O isotopic compositions of 190 seawater samples collected from the Amundsen Sea during the 34th Chinese Antarctic Research Expedition in 2017/2018.The upper-oceanic structure(<400 m)and freshwater(meteoric water and sea ice melt)distribution in the Amundsen Sea were identified based on conductivity-temperature-depth data and the H and O isotopic composition.Antarctic Surface Water,characterized as cold and fresh with low H and O isotopic ratios,was found distributed mainly in the upper~150 m between the Antarctic Slope Front and Polar Front,where it had been affected considerably by upwelled Upper Circumpolar Deep Water(UCDW)between 68°S and 71°S.A three-endmember(meteoric water,sea ice melt,and Circumpolar Deep Water)mixing model indicated that waters with relatively high proportions(>3%)of freshwater generally lie in the upper~50 m and extend from Antarctica to~65°S in the meridional direction(anomalously low freshwater proportion occurred between 68°S and 71°S).Winter Water mainly occupied the layer between 50 and 150 m south of 71°S in the western Amundsen Sea.The water structure and spatial distribution of freshwater in the upper Amundsen Sea were found influenced mainly by the rates of basal and surficial melting of ice shelves,seasonal alternation of sea ice melt/formation,wind forcing,and regional bathymetry.Owing to the distance between heavy sea ice boundary(HSIB)and ice shelves is much shorter in the western HSIB than the east HSIB,the western part of the heavy sea ice boundary includes a higher proportion of freshwater than the eastern region.This study,which highlighted the distribution and extent of freshwater derived from ice(ice shelves and sea ice)melt,provides important evidence that the offshore drift pathway of cold and fresh Antarctic continental shelf water is likely interrupted by upwelled UCDW in the Amundsen Sea.

Variability of size-fractionated phytoplankton standing stock in the Amundsen Sea during summer

The size-fractionated composition of phytoplankton greatly influences the transfer efficiency of biomass in pelagic food chains and the biological carbon flux from surface waters to the deep sea.To better understand phytoplankton abundance and composition in polynya,ice zone,and open ocean regions of the Amundsen Sea Sector of the Southern Ocean(110°W-150°W),its size-fractionated distribution and vertical structure are reported for January to February 2020.Vertical integrated(0-200 m)chlorophyll(Chl)a concentrations within Amundsen polynya regions are significantly higher than those within ice zone(t test,p<0.01)and open ocean(t test,p<0.01)regions,averaging 372.3±189.0,146.2±152.1,and 49.0±20.8 mg·m^(−2),respectively.High Chl is associated with shallow mixed-layer depths and near-shelf regions,especially at the southern ends of 112°W and 145°W.Netplankton(>20μm)contribute 60%of the total Chl in Amundsen polynya and sea ice areas,and form subsurface chlorophyll maxima(SCM)above the pycnocline in the upper water column,probably because of diatom blooms.Net-,nano-,and picoplankton comprise 39%,32%,and 29%of total Chl in open ocean stations,respectively.The open-ocean SCM migrates deeper and is below the pycnocline.The Amundsen Sea SCM is moderately,positively correlated with the euphotic zone depth and moderately,negatively correlated with column-integrated net-and nanoplankton Chl.

Effects of sea ice melt water input on phytoplankton biomass and community structure in the eastern Amundsen Sea

Sea ice melt water and circumpolar deep water(CDW)intrusion have important impacts on the ecosystem of the Amundsen Sea.In this study,samples of nutrients and phytoplankton pigments from nine stations in the eastern Amundsen Sea were collected during the austral summer.Based on in-situ hydrological observations,sea ice density data from satellite remote sensing,and chemical taxonomy calculations,the relationships between environmental factors and phytoplankton biomass and community structure were studied.The results showed that with increasing latitude,the contribution of sea ice melt water(MW%)and the stability of the water body increased,and the depth of the mixed layer(MLD)decreased.The integrated concentration of chlorophyll a(Chl-a)ranged from 21.4 mg·m^(−2) to 148.4 mg·m^(−2)(the average value was 35.7±53.4 mg·m^(−2)).Diatoms(diatoms-A[Fragilariopsis spp.,Chaetoceros spp.,and Proboscia spp.]and diatoms-B[Pseudonitzschia spp.])and Phaeocystis antarctica were the two most widely distributed phytoplankton groups and contributed 32%±16%and 28%±11%,respectively,of the total biomass.The contributions of Dinoflagellates,Chlorophytes,Cryptophytes,the high-iron group of P.antarctica,and Diatom group A were approximately 17%±8%,15%±13%,9%±6%,5%±9%,and 3%±7%,respectively.The area with the highest phytoplankton biomass was located near the ice-edge region,with a short time lag(T_(lag))between sampling and complete sea ice melt and a high MW%,while the area with the second-highest Chl-a concentration was located in the area affected by the upwelling of CDW,with thorough water mixing.Vertically,in the area with a short T_(lag) and a shallow MLD,the phytoplankton biomass and proportion of diatoms decreased rapidly with increasing water depth.In contrast,in the region with a long T_(lag) and limited CDW upwelling,the phytoplankton community was dominated by a relatively constant and high proportion of micro phytoplankton,and the phytoplankton biomass was low and relatively stable vertically.Generally,the phytoplankton community structure and biomass in the study area showed high spatial variation and were sensitive to environmental changes.

Horizontal distribution of tintinnids(Ciliophora)in surface waters of the Ross Sea and polynya in the Amundsen Sea(Antarctica)during summer 2019/2020

Information on tintinnid horizontal distribution in the Antarctic Continental Zone is scarce.During the summer of 2019/2020,tintinnid diversity and horizontal distribution in surface waters were investigated in the Ross Sea and Amundsen Sea polynya.Eight tintinnid species were found and the dominant species showed obvious horizontal distribution characteristics.In the Ross Sea,three tintinnid community groups were identified.Cymatocylis cristallina and Laackmanniella prolongata(group I)were dominant species and were mainly distributed in stations closer to the coast than were species in the other two groups.Codonellopsis gaussi(group II)and Cy.convallaria(group III)were mainly distributed in nearshore and offshore stations,respectively.In the Amundsen Sea polynya,the dominant species Cy.cristallina,L.prolongata and Salpingella faurei(group I)were mainly distributed in stations closer to the coast than were species in the other two groups.Cy.convallaria(group III)was mainly distributed in offshore stations.The distribution area where C.gaussi and C.cristallina were found in high abundance and abundance proportion of loricae with protoplasts was divided by the approximate boundary of the Antarctic Slope Front Current and Coastal Current in the Ross Sea.The highest abundance proportion in the Ross Sea was the 32-36μm lorica oral diameter(LOD)size class(75.7%),and the 36-40μm LOD size class(56.0%)was found in the Amundsen Sea polynya.Temperature-salinity-plankton diagrams of the two seas revealed that temperature may be the main reason for species distribution.Our results contribute to a better understanding of horizontal distribution of the microbial food web,and serve as a baseline for future studies of pelagic community change in the Antarctic Continental Zone.

Distribution of transparent exopolymer particles and their response to phytoplankton community structure changes in the Amundsen Sea,Antarctica

To understand the response of transparent exopolymer particles(TEP)to the changes in phytoplankton communities caused by melting sea ice,we collected samples from the polynya and open ocean affected by the Antarctic circumpolar current in the Amundsen Sea.TEP,pigments,and other environmental factors were analyzed.The results showed that high TEP content was mainly found in the polynya,and was higher in the surface layer than in the deep layer.The main factor that affected TEP distribution was the phytoplankton community.In the polynya area,the phytoplankton were dominated by low-iron Haptophyta.In the Antarctic circumpolar current region affected by ice-melting water,the dominant species was diatom type II.Our results revealed that low-iron Haptophyta may be the main contributors to TEP content.

Relating the composition of continental margin surface sediments from the Ross Sea to the Amundsen Sea,West Antarctica,to modern environmental conditions

Investigating the multiple proxies involving productivity,organic geochemistry,and trace element(TE)enrichment in surface sediments could be used as paleoenvironment archives to gain insights into past and future environmental conditions changes.We present redox-sensitive TEs(Mn,Ni,Cu,U,P,Mo,Co,V,Zn,and Cd),productivity-related proxies(total organic carbon and opal),and total nitrogen and CaCO_(3) contents of bulk surface sediments of this area.The productivity proxies from the shelf and coastal regions of the Ross and the Amundsen seas showed that higher productivity was affiliated with an area of nutrient-rich deep water upwelling.The upwelling of weakly corrosive deep water may be beneficial for preserving CaCO_(3),while highly corrosive dense water,if it forms on the shelf near the coastal region(coastal polynya),could limit the preservation of CaCO_(3) in modern conditions.There were no oxic or anoxic conditions in the study area,as indicated by the enrichment factors of redox-sensitive TEs(Mn,Co,and U).The enrichment factor of Cd,which is redox-sensitive,indicated suboxic redox conditions in sediment environments because of high primary productivity and organic matter preservation/decomposition.The enrichment factors of other redox-sensitive TEs(P,Ni,Cu,V,and Zn)and the correlations between the element/Ti ratio with productivity and nutrient proxies indicated that the organic matter decomposed,and there was massive burial of phytoplankton biomass.There was variation in the enrichment,such that sediments were enriched in P,Mo,and Zn,but depleted in Ni,Cu,and V.

Comparison of ship-based CTD measurement of Circumpolar Deep Water in the Amundsen Sea based on World Ocean Database

We compare the characteristics of Circumpolar Deep Water(CDW)in the Amundsen Sea based on Conductivity-Temperature-Depth(CTD)records in the World Ocean Database.There are considerable numbers of ship-based CTD casts in the year 1994,2000,2007 and 2009.After confining temporal-and spatial-windows,several stations are emerged as having at-least two casts in different years.The comparisons show that the CDWs turn warmer and salter on shelf and near ice shelf.The results therefore describe the geographic differences of CDW changes,and exhibit rareness of ship-based CTD survey in the Amundsen Sea.

南极阿蒙森海冰间湖的时空变化及其影响因素

本文利用由卫星微波辐射计数据反演获得的薄冰厚度和产冰速率数据,分析了南极阿蒙森海冰间湖(Amundsen Sea Polynya,ASP)在2003—2010年和2013—2020年期间的时空变化特征,结合大气再分析数据中的表面风速和气温数据,进一步探究了影响阿蒙森海冰间湖变化的因素。研究表明,阿蒙森海冰间湖位于斯维茨固定冰舌(Thwaites Fast-ice Tongue,TFT)以西的沿岸海域,大体呈现反L形,即在风的作用下,阿蒙森海冰间湖从TFT西侧向西发展,从多特森冰架(Dotson Ice Shelf,DIS)沿岸向北发展。此外,阿蒙森海冰间湖在南极冬半年的4—10月期间基本维持开放状态,但是其面积与产冰速率在相邻的两天常常发生大幅度变化,并且与其上空的风速之间具有良好的相关性。研究发现,东风分量通过调节冰间湖内部海冰的输运,主导了阿蒙森海冰间湖的面积变化;南风分量携带来自DIS沿岸陆地的冷空气加剧阿蒙森海冰间湖表面的热损失,是冰间湖产冰速率增加的决定因素。

Modified Circumpolar Deep Water inflow to the Dotson-Getz Trough in the summers of 2020 and 2022

The melting of the West Antarctic Ice Shelf has increased since the 1990s,driven by the relatively warm Circumpolar Deep Water(CDW)that penetrates into the West Antarctic Ice Shelf cavities through submarine glacial troughs across the continental shelf.In this study,temperature,salinity,and current velocity data obtained by the Chinese National Antarctic Research Expedition in the Dotson-Getz Trough(DGT)shows clear differences in distribution of modified Circumpolar Deep Water(mCDW)in the summers of 2020 and 2022.Combined with contemporaneous wind data and additional temperature and salinity data from instrumented seals,the processes and mechanisms responsible for this variation are discussed.Compared with 2020,there is a significant increase in mCDW thickness in 2022,with a doubling of total heat content as the mCDW inflow path across the DGT shifts towards the eastern bank.We propose that a southward shift in the westerly winds in the summer of 2022 moved the upper oceanic divergence zone southward towards the continental slope,promoting the upwelling of mCDW above 500 m.Concurrently,stronger westerly winds over the continental slope strengthened the eastward undercurrent,increasing the transport of this mCDW and its associated heat content to the DGT through Ekman dynamics.These observations show there is strong interannual variability in the strength,path and extent of mCDW inflows to the DGT and that care must be taken when planning observation programs for long-term monitoring of the oceanic heat input to the ice shelves of this globally significant region.

晚更新世阿蒙森海生产力和冰筏输入的变化对表层海洋环境和西南极冰盖演化的指示

阿蒙森海是当前全球变暖背景下西南极冰盖消融的核心区域。本文分析了中国第34次南极考察采集自阿蒙森海的ANT34-A5-7岩芯中生产力和冰筏碎屑含量等指标,旨在重建研究区深海氧同位素MIS 6期以来表层海洋环境和西南极冰盖演化历史。研究结果显示,阿蒙森海生产力呈现间冰期高、冰期低的特征。在末次间冰期(MIS 5.5)具有比当前更高的生产力水平,同时伴随着西南极冰盖的严重消融。这个现象归因于MIS 5.5更暖的海表温度、更少的海冰覆盖,以及向南入侵的绕极深层水的上涌。该研究结果可对预测未来气候变化提供必要的理论依据。

SAM和ENSO对罗斯海和阿蒙森海区域冬季气候的影响

本研究利用ERA5数据对南半球环状模(SouthernAnnularMode,SAM)正、负位相和ENSO(El Ni?o-SouthernOscillation)事件发生时罗斯海和阿蒙森海冬季风场、气温和海平面气压进行合成分析,并深入分析了SAM和ENSO对冬季阿蒙森低压(Amundsen Sea Low,ASL)的影响,通过对典型区域进行经验正交分解(Empirical Orthogonal Function,EOF),结合ASL中心的位置变化,解释了SAM和ENSO事件同时发生时该区域风场的变化特征。结果表明,在罗斯海和西阿蒙森海,主要由SAM和ENSO通过影响ASL的纬向位置来影响该区域的风场,当SAM正位相和拉尼娜事件同时发生时,ASL的位置显著靠东,造成了西罗斯海南风减弱,东罗斯海南风加强,西阿蒙森海沿岸东风减弱。而在东阿蒙森海,主要由SAM通过影响ASL的经向位置来影响该区域的风场,SAM负位相时,ASL中心位置靠北会造成东阿蒙森海东风增强。此外,ASL位置的偏移也会造成该区域大气环流的改变,当SAM正位相和拉尼娜事件同时发生时,ASL偏移至西阿蒙森海沿岸,而从南极大陆来的寒冷气流主导了该区域,造成气温异常降低,降幅最大超过3℃。

基于MaxEnt和GARP的阿蒙森海域南极磷虾(EUPHAUSIA SUPERBA)的分布区预测

南极磷虾是南大洋生态系统的关键物种,在南极碳汇过程中起到重要作用,近年来受到越来越多的关注。针对位于南大洋太平洋扇区的阿蒙森海域,运用最大熵模型(maximum entropy modeling,MaxEnt)和预设规则的遗传算法(genetic algorithm for rule-set production,GARP)两种生态位模型,基于已采集的南极磷虾分布点的数据,对其在阿蒙森海域的潜在分布区进行了预测和分析,并采用受试者工作特征曲线(receiver operating characteristic curve,ROC)下的面积(area under curve,AUC)和真实技巧统计法(true skill statistic,TSS)对模型结果进行评估。结果表明:MaxEnt模型中的高适生区刻画细致,GARP模型预测的高适生区分布范围更广。为克服单个模型的不确定性得到更佳结果,将两个模型的预测结果进行集合。集合后的结果模拟精度显著提高(AUC为0.946,TSS为0.78),达到了极好的预测效果。磷虾的高适生区集中分布在65°~73°S,占总面积的6.2%,中适生区占总面积的5.7%。海冰、平均海平面气压最小值和纬向流速最大值是MaxEnt中贡献最高的3个变量,3个变量贡献达81.3%。相较于MaxEnt模型,GARP模型中各个变量遗漏误差相对较平均。研究表明,集合的结果能够提高物种分布预测的准确性,阿蒙森海域南极磷虾的分布预测结果可以为磷虾保护、利用提供科学参考。