The composition and origination of particles from surface water in the Chukchi Sea, Arctic Ocean

●Article●Advances in Polar Sciencedoi: 10.13679/j. advps.2014.3.00147September 2014 Vol. 25 No. 3: 147-154The composition and origination of particles from surfacewater in the Chukchi Sea, Arctic OceanYU Xiaoguo*, LEI Jjiang, YAO Xuying, ZHU Jihao & JIN XiaobingKey Laboratory of Submarine Geosciences, Second Institute of Oceanography, SOA, Hangzhou 310012, ChinaReceived 19 April 2014; accepted 26 May 2014Abstract Suspended particle samples were collected at 11 stations on the shelf and slope regions of the Chukchi Sea and thecentral Aretic Ocean during the fifth Chinese National Arctic Research Expedition (summer 2012). The particle concentration,total organic carbon (TOC), total nitrogen (TN) and the isotopic composition of the samples were analyzed. The suspended particleconcentration varied between 0.56 and 4.01 mgL); the samples collected from the sea ice margin have higher concentrations.The organic matter content is higher in the shelf area (TOC: 9.78% 20.24%; TN: 0.91%- 2.31%), and exhibits heavier isotopiccompositions (8"C:- -23.29%o to- -26.33%o PDB; δ'N: 6.14%0-7.78%o), indicating that the organic matter is mostly marine inorigin with some terrigenous input. In the slope and the central Arctic Ocean, the organic matter content is lower (TOC: 8.06%-8.96%; TN: 0.46%-0.72%), except for one sample (SR15), and has lighter isotopic compositions (8"C: -26.93%o to -27.78%oPDB; δ'N: 4.13%o- 4.84%o). This indicates that the organic matter is mostly trrstrially derived in these regions. The extremelyhigh amount of terrigenous organic matter (TOC: 27.94%; TN: 1.16%; 8δIC: -27.43%0 PDB; 8'SN: 3.81%o) implies that it wascarried by transpolar curents from the East Siberian Sea. Material, including sea ice algae, carried by sea ice are the primarysource for particles in the sea ice margins. Sea ice melting released a substantial amount of biomass into the shelf, but a largeamount of detrital and clay minerals in the slope and the central Arctic Ocean.Keywords Chukchi Sea, particles, organic matter, stable isotopesCitation: YuX G, LeiJJ, Yao X Y, et al. The composition and origination of particles from surface water in the Chukchi Sea, ArcticOcean. Adv Polar Sci, 2014, 25: 147-154, doi: 10.13679/j.advps.2014.3.001471 Introductionnarrow Bering Strait between Alaska and Siberia, and theTranspolar Current that inputs large volumes of fresh waterThe Arctic Ocean is almost completely surrounded by theand terrigenous material from the East Siberian, Laptev andEurasian and the North American continents. It is connected Kara Seas. The sea ice cover in the Arctic Ocean reaches itsto the Pacific Ocean via the Bering Strait and to the Atlanticmaximum in March, and minimum in September!". Sea iceOcean through the Fram Strait. Shallow continental shelfin the Chukchi Sea is seasonal with melting starting in July;regions account for ~50% of the total surface area of theit is covered completely in December2.Arctic Ocean, which makes it unique among the world'sGlobal warming in the Arctic is decreasing the extentoceans. The Chukchi Sea is a marginal sea of the Arcticand thickness of sea ice cover, increasing the ice free seasonOcean. It is bounded on the west by the East Siberian Sea,in the Arctic Ocean. The changing climate is also alteringto the east by Alaska and the Beaufort Sea, and to the norththe timing and magnitude of river discharge and coastalby the Chukchi Plateau and Canadian Abyssal Plain. The erosion, and the delivery of trigenous organic cartbon to theBering Strait is its southernmost limit and connects it to theArctic Ocean. Recently, many scientists (funded by differentBering Sea and the Pacific Ocean. Its surface currents includecountries) investigated global changes in the Arctic Ocean.the warm and relatively saline water originating from theFor example, the US National Science Foundation (NSF)-funded Shelf- B中国煤化工:$ project aimedto provide a tho二_current status of* Corresponding author (email: yuxiaoguo@sio.org.cn)the Chukchi/BefYHc N M H Ggional focus onjournal.polar.gov.cn148YU X Q, et al. Adv Polar SciSeptember(2014) Vol. 25 No. 3the outer shelves and slopes. Aditional projects included 2 Materials and methodsthe Russian- American Long-term Census of Marine Life2.1 Samples(RUSALCA) and Bering Strait Environmental Observatory(BSEO). The Chinese National Arctic Research ExpeditionSuspended particle samples were collected at 11 stationsalso has sponsored five expeditions since 1999. Suspendedon the shelf and slope regions of the Chukchi Sea andparticle sources and composition could therefore be of greatthe central Arctic Ocean during the 5th Chinese Nationalinterest to scientists because it aids in the understandingArctic Research Expedition (July- September 2012; Tableof depositional processes, primary production and carbon1). Samples were collected from stations R02, CC2, CC5,cycling.CC7, R04 and RO5 in July. The station RO5 is located on theIn the Chukchi Sea, organic matter mainly derives fromsea ice margin, while the others are located in the open sea.the marine environment, but contains contributions from theSamples were collected from stations ICE01, ICE05, SR18,Yenisei, Ob and Yukon riversI3+1. Primary production fromSR15 and M01 in late August September. Station M01 issea ice contributes significantly to biogeochemical cycles located in the open sea, while the others are located on thein Arctic waters and the stable isotopic composition of thesea ice margin (Figure 1).ice-derived material differs from pelagic-derived material.The surface (<1 m) water samples were filtered on boardThis difference can be used to assess cryopelagic- -benthic the ship through a pre-weighed and pre-combusted (400"C, 4 h)coupling5-1I. The influence of sea ice contribution on theWhatman glass fiber filter (GF/F; 0.7 um). After filtration, thebiochemical cycles and depositional processes has been afilters were washed 3 times with 20 mL of deionized water totopic of interest over the last decade9-1I.remove salt and then stored (- -20C ). After the expedition, theIn the western Arctic Ocean, research on marine filter samples were freeze-dried and re-weighed to determinebiology, chemical oceanography and marine geology has beenthe particle concentration.carried out by Chinese scientists since the late 1990s. SomeThe filters were exposed for 24 h to concentrated HCIof the publication topics included: the short-term flux andfumes, then washed with deionized water to remove inorganiccomposition of particulate organic matter 10; phytoplankton carbon, and finally analyzed for total organic carbon (TOC),spatial variationl"3); chlorophyll-a and primary productivityl14total nitrogen (TN), δ'C and δ'N.characteristics of the water chemistrylus; organic carbonburial efficiencyl;, organic isotopic composition in surface2.2 Organic matter elemental and stable isotopicsediments; sedimentary environmental changesl17] andcompositionspaleoceanographylThe primary objectives of our study were to understandTOC, TN, stable carbon and nitrogen isotopic compositions werethe composition and origin of surface particles and evaluatemeasured on a Thermal-Finnigan Delta plus AD mass spectro-the sea ice contribution to these particles. To this end，meter Conflo III interfaced with an elemental analyzer (EA112).we analyzed particle concentration, viewed the composition,Organic standards (USGS-24, GBW4408 and IAEA N1) hadand traced the organic matter origin based on itsa precision of +0.2% for δ'C and +0.3% for δ'N and the .elemental (TOC and TN) and stable isotope (δ"C and δI'N) relative analytical reproducibility was 20%. For abnormalcomposition.results, parallel samples were analyzed to confirm the data.0°N5●ICE0185 °N●ICE0580°NSR1575°1Laptev SedChukchi Sea●R0570° N.R04中国煤化工120°E150°E180°EYHCNM HGFigure 1 Location of sampled stations and distribution of surface currents (gray linel19). The arrows indicate current directionality.The composition and origination of particles from surface water in the Chukchi Sea, Arctic Ocean149Table 1 The suspended particle concentration of the Chukchi Sea2.3 SEM-EDSand the central Arctic OceanScanning electron microscopy (SEM) was performedNo. Stations Depth/mConcentration/RegionsSamplingwith a Zeiss Ultra 55 coupled to energy dispersive X-ray(mgL")datespectroscopy (EDS; OXFORD X-MAX 20); Emission1.0520120718voltage: 15 kV; Pt film.51.11.24201207193 Results28.90.83Chukchi3.1 Surface water particle concentration45.30.56ShelfThe surface water particle concentrations varied between6 R0536.91.41201207200.56 and 4.01 mg:L' with an average value of 1 .54 mgL'.22770.6820120906Samples collected from the sea ice margin have higherSR1530901.67201 20905Slopeconcentrations, and the samples collcted from onshore areSR1833931.7120 120904higher than those offshore. In the shelf area, the particle10 ICE0531804.01the central 20120902concentrations nearer the coast (stations R02, CC2, CC5and CC7) are clearly different than further offshore (station11 ICE012.78Arctic Ocean 20120829R04). Additionally, the particle concentration is 2.5 timeshigher at the sea ice margin (station R05) than in open water(station R04). On the slope and in the central Arctic Ocean,SR15 and ICE05 were examined by scanning electronmost of the stations located at sea ice margins exhibit highermicroscopy (SEM) to determine the particle composition.particle concentrations, except for station M01, which isIn general, the particles were composed of well- preservedlocated in the open sea (Table 1 and Figure 1). The particlebiomass (algae), bio-debris, detrital and clay minerals. Spatialconcentration distribution suggests that terrigenous materialvariations were observed in the particle composition becausehigher biomass content and fewer detrital and clay mineralscarried by sea ice is the main particle source.were found in the shelf stations (R02, CC7 and R05).Biomass included disco, bally, rosary and leaf-like algae3.2 Particle compositionwith sizes generally <20 um, and preserved microstructuresThe samples collected from stations R02, CC7, RO5, M01,formed in situ (Figures 2a- 2h).a Alga and detrital minerals (station CC5)b Detrital minerals and alga (station CC5)中国煤化工YHCNMH Gc Algae (station R02)d Algaae (station R05)150YU X Q, et al. Adv Polar SciSeptember(2014) Vol. 25 No. 3e Alga and detrital minerals (station R05)f Algae (station R05)巴g Algae (station R05)h Algae (tation R05)国，EEi Detrital minerals and alga (station ICE05)j Sitiflallale (station ICE05)中国煤化工k Algae (station ICE05)IDetrital miTYHCNMH GThe composition and origination of particles from surface water in the Chukchi Sea, Arctic Ocean151m Detrital minerals and alga (station SR15)n Clay mineral (station M01)o Alga and algal fragments (station M01)p Algac, algal fragments and detrital minerals (station M01)Figure 2 SEM image of suspended particles (a- h, shelf; i- p, slope and central Arctic Ocean).Terrigenous detrital minerals, some clays and littleTable 2 TOC, TN, C/N ratio and isotopic composition ofbiomass were observed at the sea ice margin stations (ICE05suspended particlesand SR15) on the slope and in the central Arctic Ocean. SeaNo. Stations TOC/% TN/% CN(wt%) 8C/ (%o PDB) 8'N%ice carried the less rounded, mixed-size detrital minerals.There is lttle well-preserved biomass (algae). The biomassR02 20.24 2.3 18.8-23.967.55consisted of predominantly two types, slightly pigmentedCC11.21 1.42-24.946.96ones >40 μm and transparent ones with microstructurescC5 12.29 1.796.9-24.926.7<5 um. In addition, pigmented radiolarians were found. The14.82 1.78well-preserved biomass content is higher in the open waterRO4 13.02 1.588.2-26.336.66station M01 (Figures 2i- 2p).7.783.3 Organic matter elemental and stable isotopicM018.96 0.712.4-27.784.84SR1527.94 1.163.81compositionsSR18 8.69 0.4618.9-27.684.21The TOC values varied from 8.06% to 27.99% and 73% of10 ICE05 8.06 0.5115.8- 26.934.13samples fell within 8%-14%. The TN vales ranged from11 ICE01 8.86 0.5316.7-27.064.77_0.63% to 2.3% and most of the samples fell within either0.5%-1.0% or 1.5%- 2.0%. The C/N ratio ranged from 6.9(Station CC5) to 24.1 (Station SR15). Most samples fell and 3.65% -4.84%, respectively. These data agree well withwithin two ranges: 8- 10 and >15. Except for station RO5 atpreviously reported values from this ara3-20-2.the sea ice margin, the CN ratio is <9 in the shelf area andThere was a significant correlation between TOC andwith the exception of station M01 in open water, it is>15 onTN, and 8*C and δ'N (Figures 3a, 3b). The coefficient ofthe slope and in the central Arctic Ocean (Table 2).correlation, R, is 0.928 between 8*C and δIN and 0.926 forThe isotopic composition is characterized by enrichedTOC and TN. The only exception is the sample from station'C and I'N in the samples collected from areas withoutSR15. These correlation coefficient values suggested thatsea ice. The 88C and δIN values ranged from -23.29% to these parameters"中国煤化工: fators, so that-26.33%o PDB and 6.149%-7.78%0, respectively. The '2C and TN represents (rganic nitrogenI4N is enriched in the samples from the sea ice margin. Theis negligible orMHC N M H Gc carbon during8}C and δ'°N values ranged from -26.93%o to -27.78%o PDB sample pre -processing. This result is inconsistent with particle152YU X Q, et al. Adv Polar SciSeptember(2014) Vol. 25 No. 3data from the Kara Sea and the Canadian Arctic OceanB-4, but indicated the particles were distributed uniformly on the filter.not with surface sediments from the Yermark Plateaul23] andChukchi Sal0.Table 3 Parallel analyses of TOC, TN and their isotopicThe sample collected from station SR 15 containedcomposition in the suspended particles of station SR15extremely high TOC and TN content compared with theParallel analysis 8"C/(%o PDB) TOC/% TN/% 8'N/%oothers on the slope and in the central Arctic Ocean. Parallelanalyses were carried out to dismiss the errors caused by-27.6426.201.113.56analysis and heterogeneous distribution. The analyses showed-27.7628.851.21 3. 75the range of TOC (26.2% -28.9%, mean 27.9%) and δ*C .-27.8228.11values (- -27.6% to -27.9%o PDB, mean - -27.8% PDB), as-27.8328.55well as TN (1.15%-1.21%) and δ°N (3.6%- 3.8%o; Table 3).-27.7827.99The analytical error fell within the allowable range and2.5r8Ay=20.16 375X-0.73 9372.020.935 887/ Y=0.865 54X+28.309 53SRI5R0.918 33仓35t/1.0-B.0.s- C)B015202530-28 -27 -26 . -25 -24 -23TOC%83C (% PDB)Figure 3 Relationship between TOC and TN and their isotopic composition.enriched in the light isotope and isotopic enrichment under4 Discussionlow nutrient (or nutrient limited) conditiosn1l16.1823-24.The isotopic composition of C and N and the ratio of CIN4.1 Particle sources in surface waterare often used to determine the relative contributionof terrigenous and marine organic matter in suspendedIn general, the 8'C and 8N values of particulate organicparticulates as well as environmental fluctuations. Marinematter are influenced by the isotopic values of nutrients in thephytoplankton have 8"C values between -19%o and -25%surface water. In the Arctic Ocean, the 8C and δ'N valuesPDB, δ°N values between 4%o- -6%o and CN ratios from 7of particulate organic matter ranged from -26%o to -2 1%oto 10. The 8"'C values of lcustrine algae are between -25% PDB and 3.5%o- -10.6%o, respetitily921.. According to theand- -30%o PDB. The δC value of C3 plants is about -27%odata obtained from the RUSALCA Second Expedition, thePDB, while C4 plants average - 14%o PDB. Vascular plantaverage δ'C value of particulate organic matter is -24.5%material has significantly higher C/N ratios (20- >50), while PDB in the East Siberian Sea and between -22.2%o andbacterioplankton are nitrogen-rich and therefore have CIN23.4%o PDB in the Chukchi Seal2"!.ratios from 2- 5. In general, the range of δ'N is broader withBased on the relationship of TOC and TN and of δ°Cmarine organisms exhibiting heavier δ'N values than thoseand δI°N values, particles can be divided into two groups:on land.Group A (shelf samples) and Group B (slope and the centralThe Arctic Ocean has a special geography because it isArctic Ocean; Figure 3). Group A contains higher TOC andseparated from the other oceans and covered by sea ice forTN content and heavier C and N isotopic compositions,long periods of time. Therefore, fluvial terrigenous input andwhich indicates that organic matter predominantly originatedsea ice algac are very important organic sources. In addition, from the marine realm with a small contribution from thethe differences found among the CN ratios, δ"C and δ'Nterrestrial realm. In contrast, Group B exhibits lower TOC andvalues of particles from the Laptev, Kara and Beaufort SeasTN content, lighter C and N isotopic compositions, and theresulted from terrestrial vegetation and nutrient input-41.organic matter is mainly composed of terrigenous material.In the Arctic Ocean, light availability and nutrient These data agree well with the SEM observations.supply are the most important factors controlling primaryIt is interesting to note the differences in TOC, TN, δ°Cproduction, including sea ice algaelb.,9. It was shown thatand δ'5N from the stations RO5 and SR15. In R05, the isotopicthe I'N/4N ratio of particulate organic matter has a closecompositions are中国煤化ibut its TOC andrelationship with nutrient (NO) uilization in the overlying TN content belorwas collected atsurface waters. In the photic zone there is preferential uptakethe sea ice margYHC N M H G (sampling date:of l4NO; by phytoplankton producing photosynthetic products20 July 2012), so the lower organic matter content may beThe composition and origination of particles from surface water in the Chukchi Sea, Arctic Ocean153a result of the plankton not blooming at that time coupledThe particulate δ}C is ~3%o is heavier in the seawith depleted nutrient content from the Bering Strait currentice margin station (R05) than in the adjacent open waterowing to plankton growing in the southern arel5.251. Thestation (R04) on the shelf. The difference is less than 0.9%onutrient conditions limited plankton growth, which resultedon the slope and in the central Arctic Ocean. These resultsin lower organism content and heavier isotopic composition also suggested that sea ice algae contribute significantly toin the sample. Additionally, these may reflect sea ice algaeparticles on the shelf, but not on the slope and in the centralcontributions to the particulate material (see details below).Arctic Ocean.In SR15, the CN ratio has an abnormally high value and thecorrelation ofTOC and TN departed from the main trend, but 5 Conclusionsthe isotopic composition is characteristic for Group B (Figure3). Station SR15 is located at the Chukchi slope, where theThe surface water particle concentration is higher on theTranspolar Current carries large volumes of fresh water andshelf and the sea ice margin. In samples collected fromterrigenous material from the East Siberian, Kara and Laptev the shelf area, the organism content is higher and algaeSeas (Figure 1). Particulate organic matter in the surface microstructures were in situ properties. Samples collectedwater showed lighter 8'C values (-25.2%o to -31.0% PDB),from the slope and the central Arctic Ocean contain mainlyand there was a positive correlation of salinity with 8δ'Cl9.detrital and clay minerals and biomass fragments carried byThe CN ratios are between 11.7 and 29.2 (Laptev Sea) andsea ice with a lower organism content.11.7 and 17.5 (Kara Sea)Bl. These organic matter propertiesThe organic matter sources were mixed in the studyare consistent with our results. The extra source of terrigenousarea. The organic matter is mostly marine with someorganic material in station SR15 is thus thought to originate terrigenous input in the shelf area and mostly terrigenous onfrom the Transpolar Current.the slope and in the central Arctic Ocean.Material carried by sea ice contribute significantly to4.2 Sea ice contribution to particulate materialparticles in the surface water. The melting of sea ice releaseda substantial amount of biomass on the shelf, but a largeIn the study area, the surface water particle sources include: amount of detrital and clay minerals and lttle biomass on theterrigenous material carried by rivers; airborne particulates inslope and in the central Arctic Ocean.areas free of sea ice; biogenic matter carried by sea ice alongwith algae living in the sea ice. Recent research suggestedAcknowledgments We greatly acknowledge the outstanding supportthat interactions between sea ice, the water column andwe received from our cllagues during the fifth Chinese National Arcticbenthos are strongly enhanced during ice melt. Ice melt leadsResearch Expedition, who helped us with the field sampling program. Weto a freshening of the ocean surface layer and an initiationthank the fllows of the project CHINARE-03-02, and anonymous reviewersof the spring phytoplankton bloom, and also to a biomasswho helped improve this manuscript. This study was funded by the ChinesePolar Environment Comprehensive Investigation and Assessment Programrelease, which is an important early food source for pelagic(Grant no. CHINARE-03-02).and benthic herbivores!'o. The sea ice melting in the Chukchiregion releases a substantial amount of organic material fromReferencesthe ice, which contributes both to phytoplankton seeding andthe nutrition of zooplankton and benthoslo.Perovich D K, Richter-Menge J A. Loss of Sea Ice in the Arctic.In the shelf area, the particle concentration is higher atAnnual Review of Marine Science, 2009, 1: 417-441station RO5, which is located at the sea ice margin. The algae2 Wang M Y, Overland J E, Stabeno P. Future climate of the Bering andcontent is higher and contains well-preserved microstructuresChukchi Seas projected by global climate models. Deep- Sea Research(Figures 2c- -2h), which implies the origin was biomassII, 2012, 65(70): 46-57.released from the ice. 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