Migration and role of zinc in biogeochemical cycles in the Antarctic Ice Sheet and the Southern Ocean

Zinc(Zn),a widespread metal in the Earth’s crust,serves as a crucial nutrient in the Southern Ocean’s primary production.Studies on Zn in Antarctic snow and ice offer insights into the origins of this metal and its transport routes,as well as its impact on the biogeochemical processes within the Antarctic atmosphere–land–ocean system.This review examines research on the spatial and temporal distribution of Zn in Antarctic snow and ice,as well as in Southern Ocean waters.It includes an overview of advanced methods for sampling and analyzing Zn,along with explanations for the observed variations.The review also discusses various sources of Zn as a nutrient to the Southern Ocean.Finally,it addresses prospective issues related to the use of Zn isotopes in identifying atmospheric sources and their biogeochemical effects on the development of the Southern Ocean ecosystem.

Space physics and astronomy research from Chinese polar stations: current and future directions

Space weather has a remarkable effect on modern human activities,e.g.,communication,navigation,space exploration etc.Space physics study from polar stations is as an important part of the entire solar-terrestrial space,and conducts quantitative research from the perspective of overall space plasma behavior.One of the most important issues is to identify the dominant processes that transfer plasma and momentum from the solar wind to Earth’s magnetosphere.Thus,it is necessary to carry out research for combination the observations from polar ground stations and spacecraft observations in the space.Observations at polar regions can be as a window to the space for satellite traffic controls.The operation of the observation chain―Zhongshan-Taishan-Kunlun Station could monitor polar space debris in a large area with high temporal and spatial resolution.Also,night-time measurements of astronomical seeing at Dome A in Antarctica make it less challenging to locate a telescope above it,thereby giving greater access to the free atmosphere because of a thinner boundary layer.

Export of Greenland Sea water across the Mohn Ridge induced by summer storms

The Mohn Ridge separates the Greenland Sea and the Lofoten Basin.Previous studies identified the export across the Mohn Ridge(EMR)from the Greenland Basin into the Lofoten Basin using water mass analysis and the tracer diffusion method,but there is still lack of direct current measurements.A surface mooring with four current meters was deployed on the Mohn Ridge from June 5 to June 18 in 2015,when three cyclones passed in the adjacent area.In the absence of cyclones,the flow on the Mohn Ridge was northeastward,parallel to the ridge.When cyclones appeared,the EMR occurred to transport Greenland Sea water into the Lofoten Basin.The probable mechanism is the sea level height variation caused by the perturbation of the low pressure of cyclones,which yields an outward pressure gradient force to drive the outflow.Our results suggest that the outflow is intermittent and only happens during cyclone activities.The annual mean volume flux of EMR was roughly estimated by the limited data,which is about 3.8×10^(6)m^(3)/s,a little bit smaller than the estimation based on volume conservation.The results indicate that the contribution of the cyclonic storms to EMR is a greatly important mechanism that potentially influences the global thermohaline circulation through the Greenland-Scotland Ridge overflow.

Carbon isotope ratios of n-alkanoic acids: new organic proxies for paleo-productivity in Antarctic ponds

Primary productivity in the Antarctic aquatic environment with simple ecosystems is sensitive to climate and environmental fluctuations.We investigatedδ13C values for n-alkanoic acids derived from phototrophic organisms in a lacustrine sediment core(IIL3)to indicate primary productivity in ponds on Inexpressible Island in the western Ross Sea,Antarctica.Short-chain n-alkanoic acids(C14–C18)were abundant in the IIL3 sediment profile.The carbon isotope ratios of short-chain n-alkanoic acids in the sediment samples and floating microbial mats were similar,indicating that the short-chain n-alkanoic acids in the IIL3 sediment profile predominantly originated from phototrophic organisms.Theδ13C values for the short-chain n-alkanoic acids varied widely through the sediment profile,and 13C-enrichment of n-alkanoic acids was most likely related to high productivity due to carbon-limited conditions caused by enhanced photosynthetic efficiency.Theδ13C values for the n-alkanoic acids changed over the past 3200 years in similar ways to organic proxies for aquatic productivity(n-alkanoic acid and sterol sedimentary fluxes).C16 n-alkanoic acid was enriched in 13C in periods of high aquatic productivity~750–1650 and 3000–3200 a BP but depleted in 13C in periods of relatively low productivity~150–600 and 2500–3000 a BP.The results indicated that carbon isotope ratios of lipids from phototrophic organisms could be used as new proxies to reconstruct paleo-productivity in Antarctic lakes and ponds and therefore improve our understanding of past climate changes.

Potential suitable sites for the calibration of Scientific Echo Sounder in the marginal seas around Antarctica

The in situ calibration of Scientific Echo Sounders(SESs)in the Southern Ocean is crucial for accurate assessments of Antarctic krill and fishery biomasses.Because of the occurrence of strong winds,waves,and sea ice coverage in most seasons,SES calibration is usually difficult to perform in the Southern Ocean.Accordingly,it is essential to identify potential sites suitable for SES calibration in the marginal seas around Antarctica to successfully calibrate SESs in the Southern Ocean.Using synthetic analyses of the wind,surface current,and sea ice concentration in the targeted seas,we found that the polynya in the southeast Prydz Bay,close to the Chinese Zhongshan Station,is an ideal location to calibrate SESs based on its weak wind and surface current and its ice-free coverage during Antarctic cruises.Calibrations of the SESs onboard the research vessels of Xuelong and Xuelong 2 during the 36th and 37th Chinese National Antarctic Research Expeditions indicate that this location is a potential suitable site for conducting SES calibration with the vessel in a drifting mode.

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.

Physics of Arctic landfast sea ice and implications on the cryosphere: an overview

Landfast sea ice(LFSI)is a criticalcomponent of the Arctic sea ice cover,and is changing as a result of Arctic amplification of climate change.Located in coastal areas,LFSI is of great significance to the physical and ecological systems of the Arctic shelf and in local indigenous communities.We present an overview of the physics of Arctic LFSI and the associated implications on the cryosphere.LFSI is kept in place by four fastenmechanisms.The evolution of LFSI is mostly determined by thermodynamic processes,and can therefore be usedas an indicator of local climate change.We also present the dynamic processes that are active prior to the formation of LFSI,and those that are involved in LFSI freeze-up and breakup.Season length,thickness and extent of Arctic LFSI are decreasing andshowing different trends in different seas,and therefore,causing environmental and climatic impacts.An improved coordination of Arctic LFSI observation is needed with a unified and systematic observation network supported by cooperation between scientists and indigenous communities,as well as a better application of remote sensing data to acquire detailed LFSI cryosphere physical parameters,hence revolving both its annual cycle and long-term changes.Integrated investigations combining in situ measurements,satellite remote sensing and numerical modeling are needed to improve our understanding of the physical mechanisms of LFSI seasonal changes and their impacts on the environment and climate.

A simulation study of protons heated by left/right-handed Alfvén waves generated by electromagnetic proton-proton instability

Most protons in the solar wind belong to one of two different populations,the less dense beam protons and the denser core protons.The beam protons,with a velocity of(1-2)V_(A)(V_(A)is the local Alfvén speed),always drift relative to the core protons;this kind of distribution is unstable and stimulates several kinds of wave mode.In this study,using a 2 D hybrid simulation model,we find that the original right-handed elliptically polarized Alfvén waves become linearly polarized,and eventually become right-handed and circularly polarized.Given that linearly polarized waves are a superposition of left-handed and right-handed waves,cyclotron resonance in the right-handed/left-handed component heats beam/core protons perpendicularly.The resonance between beam protons and right-handed polarized waves is stronger when the beam relative density is lower,resulting in more dramatic perpendicular heating of beam protons,whereas the situation is reversed when the beam relative density is larger.

An outstanding example of cooperation between Arctic and non-Arctic countries in cryosphere and climate research: Sino-Finnish cooperation for more than 30 years

The cryosphere is interconnected with other components of the climate system through global exchange of water,energy,and carbon.Long-term sustainable and pragmatic scientific and technological cooperation on the cryosphere and climatology in polar and sub-polar regions between China and Finland began in the 1980s.The fields of bilateral cooperation include joint training of young scientists,joint field observations,climatological and ecological researches of polar and sub-polar sea ice,glaciers and frozen lakes,etc.The year 2020 marked the 70th anniversary of the establishment of diplomatic relations between China and Finland.In order to celebrate the great achievements by Chinese and Finnish scientists in the fieldsof cryosphere and climate research,the Advances in Polar Science invited scientists from both sides to jointly organize a Special Issue entitled“Sino-Finnish cooperation on cryosphere and climatology in polar and sub-polar regions”.In this Special Issue,we have collected 10 papers,with most papers created jointly by scientists of both sides.The fruitful scientific achievement is strongly benefited from the sustainability of cooperation.Monitoring,research,prediction,mitigation,and adaptation to the climate change in the polar and sub-polar regions will definitively stay in the focus for many decades to come.A new era of Finnish-Chinese scientific collaboration on cryosphere has begun.

Variability of size-fractionated chlorophyll a in the high-latitude Arctic Ocean in summer 2020

The size structure of phytoplankton has considerable effects on the energy flow and nutrient cycling in themarine ecosystem,and thus is important to marine food web and biological pump.However,its dynamics in the high-latitude Arctic Ocean,particularly ice-covered areas,remain poorly understood.We investigated size-fractionated chlorophyll a(Chl a)and related environmental parameters in the highly ice-covered Arctic Ocean during the summer of 2020,and analyzed the relationship between Chl adistribution and water mass through cluster analysis.Results showed that inorganic nutrients were typically depleted in the upper layer of the Canada Basin region,and that phytoplankton biomass was extremely low(mean=0.05±0.18 mg·m^(−3))in the near-surface layer(upper 25 m).More than 80%of Chl a values were<0.1 mg·m^(−3) in the water column(0-200 m),but high values appeared at the ice edge or in corresponding ice areas on the shelf.Additionally,the mean contribution of both nanoplankton(2-20μm)(41%)and picoplankton(<2μm)(40%)was significantly higher than that of microplankton(20-200μm)(19%).Notably,the typical subsurface chlorophyll maximum(0.1 mg·m^(−3))was found north of 80°N,where the concentration of sea ice reached approximately 100%.The Chl aprofile results showed that the deep chlorophyll maximum of total-,micro-,nano-,and picoplankton was located at depth of 40,39,41,and 38 m,respectively,indicating that nutrients are the primary factor limiting phytoplankton growth in the ice-covered Arctic Ocean during summer.These phenomena suggest that,despite the previous literatures pointing to significant light limitation under the Arctic ice,the primary limiting factor for phytoplankton in summer is still nutrient.

Research progress on inter-monthly winter temperature variation in East Asia and climate prediction

近年来,东亚冬季气温的月际间变化十分显著,冬季不同月份或不同阶段之间极端冷暖事件的转折或交替频发.由于月际间变化常常被季节平均掩盖,东亚冬季气候预测面临众多的挑战.因此,亟需研究东亚冬季气温月际间变化的特征和机理,明确其可预测性和预测来源,进而研制考虑月际变化的东亚冬季气温的有效预测方法和预测模型.本文回顾了过去5年对东亚冬季气温月际间变化的主要特征,物理过程,机制,可预测性和预测的研究进展,同时考虑了多个与气温相联系统的变化,包括冬季风,西伯利亚高压,平流层极涡.本文也进一步讨论了未来的研究前景.

Variations and relations between chlorophyll concentrations and physical-ecological processes near the West Antarctic Peninsula

The West Antarctic Peninsula(WAP)region is one of the most productive marine ecosystems in the Southern Ocean that support the food web for phytoplankton,krill spawning or recruitment and several krill consumers at higher-trophic level like penguins and Antarctic fur seals.Characterized by channels and islands,the complex topography of the WAP generates interconnected circulation patterns,strongly influencing vertical stratification,nutrient availability and distribution of marine organisms.Additionally,rapid climate change associated with major climate modes like the Southern Annular Mode(SAM)and El Niño-Southern Oscillation(ENSO)has significant effects on long-term variations of physical environments and biological production.The objective of this study is to reveal the spatial-temporal variations of phytoplankton biomass in the WAP region and the modulating physical-ecological processes.By using 9-year hydrographic and ecological data of five transects collected by the Palmer Long-Term Ecosystem Research,the horizontal and vertical distributions of several physical and ecological properties,with a particular focus on chlorophyll(Chl)concentration were explored.Regression analysis among area-averaged properties and properties at single stations was performed to reveal the relationship between the interannual variations of physical and ecological processes.The correlation results showed that Chl concentration exhibited a positive relationship with both the circumpolar deep water(CDW)intrusion and vertical stratification,but showed a negative correlation with SAM at some specific stations.However,certain processes or mechanisms may only be dominant for specific stations and not applicable to the entire region.No single physical or ecological factors have been found to significantly influence the Chl distribution throughout the WAP region,which may be attributed to the heterogeneity of sea ice conditions,geometry and hydrodynamic features as well as variations in nutrient sources.

Arctic summertime anticyclonic circulation mode and its influence on substantial sea ice depletion:a review

The summertime anticyclonic circulation mode(SACM)is related to recent substantial loss of sea ice in the Arctic.This review outlines the potential causes of the SACM and considers its influence on sea ice depletion.Local triggers(i.e.,sea ice loss and sea surface temperature(SST)variation)and spatiotemporal teleconnections(i.e.,extratropical cyclone intrusion,tropical and mid-latitude SST anomalies,and winter atmospheric circulation preconditions)are discussed.The influence of the SACM on the dramatic loss of sea ice is emphasized through inspection of relevant dynamic(i.e.,Ekman drift and export)and thermodynamic(i.e.,moisture content,cloudiness,and associated changes in radiation)mechanisms.Moreover,the motivation for investigation of the underlying physical mechanisms of the SACM in response to the recent substantial sea ice depletionis also clarified through an attempt to better understand the shifting ice-atmosphere interaction in the Arctic during summer.Therecord low extent of sea ice in September 2012 could be reset in the near future if the SACM-like scenario continues to exist during summer in the Arctic troposphere.

Mechanical and numerical models for sea ice dynamics on small-meso scale

On small-meso scale, the sea ice dynamic characteristics are quite different from that on large scale. To model the sea ice dynamics on small-meso scale, a new elastic-viscous-plastic （EVP） constitutive model and a hybrid Lagrangian- Eulerian （HLE） numerical method are developed based on continuum theory. While a modified discrete element model （DEM） is introduced to model the ice cover at discrete state. With the EVP constitutive model, the numerical simulation for ice ridging in an idealized rectangular basin is carried out and the results are comparable with the analytical solution of jam theory. Adopting the HLE numerical model, the sea ice dynamic process is simulated in a vortex wind field. The furthering application of DEM is discussed in details for modeling the discrete distribution of sea ice. With this study, the mechanical and numerical models for sea ice dynamics can be improved with high precision and computational efficiency.

Meteorological and sea ice anomalies in the western Arctic Ocean during the 2018-2019 ice season:a Lagrangian study

Rapid changes in the Arctic climate and those in Arctic sea ice in recent decades are closely coupled.In this study,we used atmospheric reanalysis data and satellite remote sensing products to identify anomalies of meteorological and sea ice conditions during the ice season of 2018-2019 relative to climatological means using a Lagrangian methodology.We obtained the anomalies along the drifting trajectories of eight sea ice mass balance buoys between the marginal ice zone and the pack ice zone in the western Arctic Ocean(~160°W-170°W and 79°N-85°N)from September 2018 toAugust 2019.The temporary collapse of the Beaufort High and a strong positive Arctic Dipole in the winter of 2018-2019 drove the three buoys in the north to drift gradually northeastward and merge into the Transpolar Drift Stream.The most prominent positive temperature anomalies in 2018-2019 along the buoy trajectories relative to 1979-2019 climatology occurred in autumn,early winter,and April,and were concentrated in the southern part of the study area;these anomalies can be partly related to the seasonal and spatial patterns of heat release from the Arctic ice-ocean system to the atmosphere.In the southern part of the study area and in autumn,the sea ice concentration in 2018-2019 was higher than that averaged over the past 10 years.However,we found no ice concentration anomalies for other regions or seasons.The sea ice thickness in the freezing season and the snow depth by the end of the winter of 2018-2019 can also be considered as normal.Although the wind speed in 2018-2019 was slightly lower than that in 1979-2019,the speed of sea ice drift and its ratio to wind speed were significantly higher than the climatology.In 2019,the sea ice surface began to melt at the end of June,which was close to the 1988-2019 climatology.However,spatial variations in the onsets ofsurface melt in 2019 differed from the climatology,and can be explained by the prevalence of a high-pressure system in the south of the Beaufort Sea in June 2019.In addition to seasonal variations,the meteorological and sea ice anomalies were influenced by spatial variations.By the end of summer 2019,the buoys had drifted to the west of the Canadian Arctic Archipelago,where the ice conditions was heavier than those at the buoy locations in early September 2018.The meteorological and sea ice anomalies identified in this study lay the foundations for subsequent analyses and simulations of sea ice mass balance based on the buoy data.

Evaluation of the relationships and uncertainties of airborne and ground-based sea ice surface temperature measurements against remotely sensed temperature records

Sea ice surface temperature(IST)is an important indicator of environmental changes in the Arctic Ocean.In this study,the relative performance of four mainstream IST records,i.e.airborne IST,infrared radiometer measured IST(IR IST),longwave radiation derived IST(LWR IST),and snow and ice mass balance array buoy derived IST(Buoy IST),were evaluated against the MODIS IST product.Bias,standard deviation(STD),and root mean square error(RMSE)were used to evaluate the data quality.Results revealed that airborne IST had the best accuracy,which was 0.21 K colder than MODIS IST,with STD of 1.46 K and RMSE of 1.47 K.Ground-based ISTs were biased with each other but all warmer than the MODIS IST.The IR IST had the best overall accuracy(bias=0.55 K;STD=1.52 K;RMSE=1.61 K),while the LWR IST was the noisiest measurement with the largest outlier data percent.Besides,co-located IR and LWR ISTs were more consistent than any type of evaluated IST against MODIS IST(correlation coefficient=0.99).Airborne and IR ISTs are thus the premier choice for monitoring the rapidly changing Arctic sea ice,together with satellite observations.