Mesozooplankton distribution and diversity from the Bering Sea shelf to the Chukchi Sea

In recent decades,environmental changes in the Arctic have aroused widespread concern around the world.To better understand ecology issues such as ecosystem dynamics,the Arctic and the subarctic regions were integrated as the“pan-Arctic”region.In this study,mesozooplankton were sampled from the Bering Sea shelf to the northern Chukchi Sea during the 10th Chinese National Arctic Research Expedition in 2019.Based on the species composition and abundance,three geographical communities were identified:the Bering Sea shelf community(BSS),the Bering Strait transitional community(BST),and the Chukchi Sea shelf community(CSS).The BSS was characterized by Bering Sea oceanic species such as Eucalanus bungii;the BST was mainly composed of the pan-Arctic distributed Calanus glacialis,meroplankton of benthos,and neritic species such as Centropages abdominalis;copepods,especially the copepodite of C.glacialis,were predominant in the CSS community.The BSS community structure was strongly affected by the inflow of Bering Shelf Water,while those of BST and CSS were determined by the recruitment of local species.The zooplankton community structure is influenced by both advection and environmental changes such as warming and a prolonged productivity period.Here,it was difficult to distinguish the changes induced by climate change from the effects of the Bering Sea Water.The key to solving this problem is the accumulation of comparable data,which requires continuous monitoring of key species such as C.glacialis and Calanus hyperboreus.

The Relationship between Melt Season Sea Ice over the Bering Sea and Summer Precipitation over Mid-Latitude East Asia

Independent datasets consistently indicate a significant correlation between the sea ice variability in the Bering Sea during melt season and the summer rainfall variability in the Lake Baikal area and Northeastern China.In this study,four sea ice datasets(HadISST1,HadISST2.2,ERA-Interim and NOAA/NSIDC)and two global precipitation datasets(CRU V4.01 and GPCP V2.3)are used to investigate co-variations between melt season(March−April−May−June,MAMJ)Bering Sea ice cover(BSIC)and summer(June−July−August,JJA)East Asian precipitation.All datasets demonstrate a significant correlation between the MAMJ BSIC and the JJA rainfall in Lake Baikal−Northeastern China(Baikal−NEC).Based on the reanalysis datasets and the numerical sensitivity experiments performed in this study using Community Atmospheric Model version 5(CAM5),a mechanism to understand how the MAMJ BSIC influences the JJA Baikal−NEC rainfall is suggested.More MAMJ BSIC triggers a wave train and causes a positive sea level pressure(SLP)anomaly over the North Atlantic during MAMJ.The high SLP anomaly,associated with an anti-cyclonic wind stress circulation anomaly,favors the appearance of sea surface temperature(SST)anomalies in a zonal dipole-pattern in the North Atlantic during summer.The dipole SST anomaly drives a zonally orientated wave train,which causes a high anomaly geopotential height at 500 hPa over the Sea of Japan.As a result,the mean East Asian trough moves westward and a low geopotential height anomaly occurs over Baikal−NEC.This prevailing regional low pressure anomaly together with enhanced moisture transport from the western North Pacific and convergence over Baikal−NEC,positively influences the increased rainfall in summer.

Difference of planktonic ciliate communities of the tropical West Pacific, the Bering Sea and the Arctic Ocean

Ciliates are important components in planktonic food webs,but our understanding of their community structures in different oceanic water masses is limited.We report pelagic ciliate community characteristics in three seas:the tropical West Pacific,the Bering Sea and the Arctic Ocean.Planktonic ciliate abundance had"bimodal-peak","surface-peak"and"DCM(deep chlorophyll a maximum layer)-peak"vertical distribution patterns in the tropical West Pacific,the Bering Sea and the Arctic Ocean,respectively.The abundance proportion of tintinnid to total ciliate in the Bering Sea(42.6%)was higher than both the tropical West Pacific(7.8%)and the Arctic Ocean(2.0%).The abundance proportion of small aloricate ciliates(10–20μm size-fraction)in the tropical West Pacific was highest in these three seas.The Arctic Ocean had higher abundance proportion of tintinnids in larger LOD(lorica oral diameter)size-class.Proportion of redundant species increased from the Arctic Ocean to the tropical West Pacific.Our result provided useful data to further understand ecology roles of planktonic ciliates in different marine habitats.

Spatial variation in grain-size population of surface sediments from northern Bering Sea and western Arctic Ocean: Implications for provenance and depositional mechanisms

In general,sediments in nature comprise populations of various diameters.Accurate information regarding the sources and depositional mechanisms of the populations can be obtained through their temporal and spatial comparisons.In this study,the grain size distribution of surface sediments from the Bering Sea and western Arctic Ocean were fitted and partitioned into populations using a log-normal distribution function.The spatial variations in the populations indicate differences in their sources and deposition mechanisms.The sediments on most of the Bering Sea Shelf originated from the Yukon River,and were transported westward by waves and currents.However,the presence of a coarser population outside Anadyr Bay was the result of Anadyr River transport.Additionally,a northward transport trend of fine suspended particles was observed on the west side of the Bering Sea Shelf.The sediments in Hope Valley in the south Chukchi Sea also originated from the Yukon River.The coarser population on the central Chukchi Sea Shelf originated from coast of Alaska to the east,not the Yukon River,and was transported by sea ice and bottom brine water.The populations of sediments from the Chukchi Basin and the base of the Chukchi Sea Slope are the result of sea ice and eddy action.Surface sediments from the western high Arctic Ocean predominantly comprised five populations,and two unique populations with mode diameters of 50–90μm and 200–400μm,respectively,were ubiquitous in the glacial and interglacial sediments.It was difficult to distinguish whether these two populations originated from sea ice or icebergs.Therefore,caution should be exercised when using either the>63μm or>250μm fractions in sediments as a proxy index for iceberg and ice sheet variation in the high Arctic Ocean.

Characteristics of water masses and bio-optical properties of the Bering Sea shelf during 2007–2009

The hydrographic and bio-optical properties of the Bering Sea shelf were analyzed based on in-situ measurements obtained during four cruises from 2007 to 2009.According to the temperature and salinity of the seawater,the spring water masses on the Bering Sea shelf were classified as the Alaskan Coast Water,Bering Sea Shelf Water,Anadyr Water,Spring Mixed Layer Water,Remnant Winter Water,and Winter Water,each of which had varying chlorophyll a concentrations.Among them,the highest chlorophyll a concentration occurred in the nutrient-rich Anadyr Water((7.57±6.16)mg/m^(3) in spring).The spectrum-dependent diffuse attenuation coefficient(Kd(λ))of the water column for downwelling irradiance was also calculated,exhibiting a decrease at 412-555 nm and then an increase within the range of 0.17-0.48 m-1in spring.Furthermore,a strong correlation between the chlorophyll a concentration and the attenuation coefficient was found at visible wavelengths on the Bering Sea shelf.Spatially,the chlorophyll a concentration was higher on the northern shelf((5.18±3.78)mg/m^(3))than on the southern shelf((3.64±2.51)mg/m^(3)),which was consistent with the distribution of the attenuation coefficient.Seasonally,the consumption of nutrients by blooms resulted in minimum chlorophyll a concentration((0.78±0.51)mg/m^(3))and attenuation coefficient values in summer.In terms of the vertical structure,both the attenuation coefficient and the chlorophyll a concentration tended to reach maximum values at the same depth,and the depth of the maximum values increased as the surface temperature increased in summer.Moreover,an empirical model was fitted with a power function based on the correlation between the chlorophyll a concentration and the attenuation coefficient at 412-555 nm.In addition,a spectral model was constructed according to the relationship between the attenuation coefficients at 490 nm and at other wavelengths,which provides a method for estimating the bio-optical properties of the Bering Sea shelf.

Seabird and marine mammal at-sea distribution in the western Bering Sea and along the eastern Kamtchatka Peninsula

Seabird and marine mammal at-sea distribution in the western Bering Sea and along the eastern Kamtchatka(Kamtsjatka)Peninsula was determined during 114 transect counts,lasting 30 min each,in September 2018.A total of 58000 seabirds were tallied,i.e.a mean value of 510 per count.The most abundant species was short-tailed shearwater:43250 individuals representing 74%of the total.Fulmar and kittiwake represented 13%and 8%of the total.Important geographical differences were noted,concerning both the number of seabird species and their abundance.The following species were tallied mainly in the northern zone(North of 60°N):fulmar(light morphs),short-tailed shearwater,Vega(herring)gull and horned puffin.In the southern zone,including Commander(Komandorski)Islands,observed species included fulmar(dark morphs),pelagic cormorant,glaucous-winged gull,red-legged kittiwake and black guillemot.The vast majority of the 100 cetaceans and 40 pinnipeds were tallied in the southern area,mainly porpoises,killer whale and humpback whale,and Largha(spotted)seal.

Spatial variability of summertime aragonite saturation states and its influencing factor in the Bering Sea

The Bering sea is susceptible to ocean acidification driven by both human activities(anthropogenic CO_(2))and distinctive natural processes.To assess the situation of ocean acidification,we investigated the spatial variability of aragonite saturation states(ΩAr)in July 2010 during the 4th Chinese National Arctic Research Expedition(CHINARE).The surface waters were all oversaturated with respect to aragonite(ΩAr>1)due to high biological removal,andΩAr ranged from 1.43 to 3.17.The relatively lowΩAr values were found in the western Bering Strait and eastern nearshore region of the Bering Sea Shelf,which were associated with the upwelling and riverine input,respectively.In the subsurface,theΩAr decreased to generally low saturation states and were observed to be strongly undersaturated(ΩAr<1)in the bottom waters with a lowest value of 0.45,which might be caused by remineralization.However,unlike prior studies,the lowΩAr values in the shallow nearshore region were still above the saturation horizon throughout the water column,which were probably counteracted by high local primary production.In the context of climate change and increasing anthropogenic CO_(2)absorption,the suppression and undersaturation ofΩAr in the Bering Sea are not only attributed to the natural processes but also the accumulation of anthropogenic CO_(2).

A Possible Mechanism for Winter Sea Ice Decline over the Bering Sea and Its Relationship with Cold Events over North America

In this study,the mechanism for the sea ice decline over the Bering Sea and its relationship with cold events over North America are investigated based on the daily ERA-Interim data during the winter(December-February)of1979-2016.The results show that the sea ice decline over western(eastern)Bering Sea is mainly contributed by(1)the strengthened southerly(southeasterly)wind near the surface,which possibly pushes the sea ice to move northward,and(2)the intensified downward infrared radiation(IR),which is closely related to the local increasing surface air temperature(SAT)and the intensified moisture convergence mostly induced by the anomalous southeasterly wind associated with an anticyclonic anomaly over the Alaska Bay.During the sea ice decline over the Bering Sea,a cold SAT anomaly is simultaneously found over North America.It is proved that the occurrence of such a cold event is driven by the atmospheric internal variation,but not the forcing of sea ice decline over the Bering Sea.This study deepens our understanding of sea ice decline and its relationship with contemporary cold events in winter.