Ice Meltwater Research Articles

Photographic records of plant phenology and spring river flush timing in a river lowland ecosystem at the taiga–tundra boundary, northeastern Siberia

AbstractArctic terrestrial ecosystems near the treeline in river lowlands are vulnerable to the changing climate and seasonal extreme events, including flooding. We set up a simple camera monitoring system to record the timings and durations of the leafy period and the spring flush of river water at three observation sites (Boydom [B]: 70.64°N, 148.15°E; Kodac [K]:70.56°N, 148.26°E; Verkhny‐Khatistakh [VK]:70.25°N,147.47°E) in the Indigirka lowland, in Northeastern Siberia. Time‐lapse digital cameras were located at seven points across the three sites. The time intervals were 1–4 or 24 hours. The minimum and maximum monitoring periods were 2 years (July 2016 to August 2018) at B and 5 years (August 2013 to July 2018) at K. One camera documented the timings of river ice melt and open water periods from the riverbank of the Kryvaya River, one of the small tributaries of the Indigirka River. The other six cameras recorded several types of ground cover typical of the area, including larch trees (Larix cajanderi), shrubs (including Salix spp. and Betula nana), forbs, mosses and graminoids in an ecosystem of sparsely forested shrublands, wetlands and riversides. The data consists of 45,617 JPEG‐format images. This dataset can be used to detect the onset and offset of the growing season and to capture the ice melt timing and water cover periods in wetlands and riversides. It may be useful in validating satellite data such as the vegetation remote sensing index for remote and little‐known areas. These data may contribute to the study of the role of high‐latitude ecosystems in global climate changes.The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2020-02.1/jalter-en. [Correction added on 7 September 2020, after first online publication: JaLTER URL has been updated.]

Metatranscriptomic and Metagenomic Analysis of Biological Diversity in Subglacial Lake Vostok (Antarctica).

A combined metatranscriptomic and metagenomic study of Vostok (Antarctica) ice core sections from glacial, basal, and lake water accretion ice yielded sequences that indicated a wide variety of species and possible conditions at the base of the glacier and in subglacial Lake Vostok. Few organisms were in common among the basal ice and accretion ice samples, suggesting little transmission of viable organisms from the basal ice meltwater into the lake water. Additionally, samples of accretion ice, each of which originated from water in several locations of the shallow embayment, exhibit only small amounts of mixing of species. The western-most portion of the embayment had very low numbers of organisms, likely due to biologically challenging conditions. Increasing numbers of organisms were found progressing from west to east, up to approximately 7 km into the embayment. At that point, the numbers of unique sequences and sequence reads from thermophilic, thermotolerant, psychrophilic, and psychrotolerant organisms increased dramatically, as did sequences from alkaliphilic, alkalitolerant, acidophilic, and acidotolerant sequences. The number of unique and total sequences were positively associated with increases in concentrations of Na+, Ca2+, Mg2+, SO42−, Cl−, total amino acids, and non-purgeable organic carbon. The numbers of unique sequences from organisms reported from soil, sediment, ice, aquatic, marine, animal, and plant (probably pollen) sources also peaked in this region, suggesting that this was the most biologically active region. The confluence of the high numbers of organisms, physiologies, and metabolic capabilities suggests the presence of energy and nutrient sources in the eastern half of the embayment. Data from the main basin suggested a cold oligotrophic environment containing fewer organisms. In addition to bacteria, both the basal ice and accretion ice contained sequences from a diverse assemblage of eukaryotes, as well as from bacteria that are known to be associated with multicellular eukaryotes.

Spatial distribution of birds and terrestrial plants in Bunger Hills

AbstractIn this paper, we synthesize recorded observations of moss, lichen and bird species in Bunger Hills, East Antarctica, and assess the role of environmental controls, including sediment, salinity, moisture and geology, on species' distributions. The distribution of snow petrels (Pagodroma nivea) appears to be associated with geology; they nest by preference in crevices in bedrock outcrops around the margins of the hills or wherever jointed cliffs are found. South polar skuas (Catharacta maccormicki) are seen throughout Bunger Hills, where they nest and prey on snow petrels. Mosses and lichens were most abundant around the ice margins where fresh snow and ice meltwater are abundant. In the central area of Bunger Hills, where the highest salt concentration in sediments is found and exposure to abrasion by wind-driven mineral sand grains and ice particles is greatest, mosses and lichens are reduced in abundance and diversity. Exposure of parts of Bunger Hills from the ice sheet throughout the Last Glacial Maximum,c.20 kabp, means that some land and lakes could have acted as regional refugia and as a locus of recolonization of other ice-free areas.

Infiltration into Frozen Silty Clay Loam Soil with Different Soil Water Contents in the Red River of the North Basin in the USA

Predicting surface runoff and flooding in seasonally frozen areas such as the Red River of the North Basin (RRB) in USA is a challenging task. It depends on the knowledge of the complex process of infiltration in frozen soil, such as phase changes of water, ice content and distribution in the infiltration zone (the top 0–30 cm of the soil profile), soil pore size distribution, soil temperature and freeze–thaw cycles. In this study, the infiltration rates into frozen soil (Colvin silty clay loam according to the United States Department of Agriculture (USDA) Classification, and Chernozem according to Food and Agriculture Organization of the United Nations (FAO) international soil Classification) were measured at three different initial water contents: permanent wilting point (PWP), θpwp; field capacity (FC), θfc; and between FC and PWP, θmid. Laboratory infiltration experiments were conducted using a Cornell sprinkle infiltrometer with three replications for each initial water content. Volumetric soil water content (θv) and soil temperature at three depths were also continuously monitored using sensors. The average infiltration rates were 0.66, 0.38, and 0.59 cm/min for three initial water contents (θpwp, θmid, and θfc, respectively). Initial infiltration into frozen soil occurred quickly in the soil with θpwp because the soil was dry. Melted ice water contributed to the total soil water content over time, so it made the initial infiltration comparatively slower in the soil with θmid. Initial infiltration was also slower in the soil with θfc because the wet soil had very small pore space, so the soil rapidly reached its saturation after the infiltration started. The Horton infiltration equation was fitted with the observed infiltration rates for the soils with three initial water contents, and the goodness of fit was evaluated by using the coefficient of determination (R2) and the root-mean-square error (RMSE). The final infiltration rates from the fitted Horton equations were 0.060, 0.010, and 0.027 cm/min for the initial water contents (θpwp, θmid, and θfc, respectively). The soil water content along the soil profile changed with the amount of infiltrating water over time. However, the initial soil water content and melt water from ice resulting from soil temperature rise regulated the change in soil water content. The amount of ice melt water contribution to soil water content change varied among the soils with different initial water contents (θpwp, θmid, and θfc, respectively). The θv changed gradually in the θpwp soil, rapidly at 0 °C in the θmid soil, and less in the θfc soil. The change in pore distribution due to freeze–thaw cycles and soil packing altered the soil hydraulic properties and the infiltration into the soil. This study can provide critical information for flood forecasting model and subsurface drainage design in the RRB.

Benthic foraminifera indicate Glacial North Pacific Intermediate Water and reduced primary productivity over Bowers Ridge, Bering Sea, since the Mid-Brunhes Transition

Abstract. The Mid-Brunhes Transition (MBT) saw an increase in the amplitude of glacial cycles expressed in ice core and deep ocean records from about 400 ka, but its influence on high-latitude climates is not fully understood. The Arctic Ocean is thought to have warmed and exhibited reduced sea ice, but little is known of sea ice marginal locations such as the Bering Sea. The Bering Sea is the link between the Arctic and Pacific Ocean and is an area of high productivity and CO2 ventilation; it hosts a pronounced oxygen minimum zone (OMZ) and is thought to be the location of Glacial North Pacific Intermediate Water (GNPIW) formation in the Pleistocene. To understand palaeoceanographic change in the region, we analysed benthic foraminiferal faunas from Bowers Ridge (Site U1342, 800 m of water depth) over the past 600 kyr, as they are uniquely well preserved and sensitive to changes in deep and surface ocean conditions. We identified and imaged 71 taxa and provide a full taxonomy. Foraminiferal preservation is markedly higher during glacials, indicating the presence of less corrosive GNPIW. The most abundant species are Bulimina exilis, Takayanagia delicata, Alabaminella weddellensis, Gyroidina sp. 2, Cassidulina laevigata, Islandiella norcrossi, and Uvigerina bifurcata, consistent with broadly high net primary production throughout the last 600 kyr. Correspondence analysis shows that the most significant Assemblage 1 comprises B. exilis, T. delicata, Bolivina spissa, and Brizalina, which occur sporadically within intervals of laminated, biogenic-rich sediment, mostly during glacials and also some deglacials, and are interpreted as indicating very high productivity. Other assemblages contain the phytodetritivore species A. weddellensis, I. norcrossi, and C. laevigata, indicative of seasonal phytoplankton blooms. Before the MBT, more numerous intervals of the very high-productivity Assemblage 1 and A. weddellensis occur, which we suggest reflect a time of more sea-ice-related seasonal stratification and ice edge blooms. Our inference of a decrease in sea ice meltwater stratification influence in the central Bering Sea after the MBT is consistent with records showing that the Arctic and Pacific Ocean warmed during glacials and suggests that high-latitude productivity and sea ice changes were an important feature of this climate event.

Treatment of electroplating wastewater using the freezing method

Wastewater produced from washing can be concentrated and reused in an electroplating bath to produce a cleaner product. Predominant methods of concentrating wastewater from electroplating washing include reverse osmosis and evaporation concentration. However, reverse osmosis cannot treat strongly acidic (pH < 2) or strongly alkaline (pH > 12) wastewaters, and the scope of its application is narrow, while evaporation uses high quantities of energy and is costly. In contrast, freezing electroplating washing wastewater incurs low cost and can be used for treating washing wastewater from various electroplating processes. In this study, supercooled water dynamic ice making (SWDIM) technology was applied for the first time to freeze and crystalize electroplating washing wastewater, followed by centrifugal separation to separate solid and liquid phases. Freezing treatment was performed on the washing water from the acid copper process (pH = 1.15), nickel plating process (pH = 5.1), and zincate zinc plating process (pH = 13.2). The results show that after primary freezing and centrifugal dehydration, the solute removal rate of ice melt water exceeded 90%, which can meet the requirements of the primary washing tank to supplement the washing water. After secondary freezing and centrifugal dehydration, the concentrated wastewater (approximately 0.14 vol of the original wastewater) can be produced, further evaporated and concentrated 2.8 times, and reused for the electroplating bath.

Interannual Variability in the Absorption and Fluorescence Characteristics of Dissolved Organic Matter in the Canada Basin Polar Mixed Waters

AbstractDissolved organic matter (DOM) absorption and fluorescence properties were investigated for seawater samples collected from the polar mixed layer (0–30 m) of the Canada Basin in 2010–2012. Sea ice concentration as well as fractions of meteoric and sea ice meltwater (fMW and fSIM) calculated from oxygen isotope ratio (δ18O) were applied to assess the importance of discrete freshwater inputs to the distribution of DOM. Parallel factor analysis identified four humic‐like (C1‐2 and C4‐C5) and one protein‐like (C3) fluorescent components in 380 excitation‐emission matrix spectra. Surprisingly, despite different sea ice cover and biological regimes, DOM composition was largely homogeneous spanning these annual surveys. A strong and reoccurring coastal influence on DOM absorption and humic‐like DOM was observed each year and was particularly pronounced during the summer 2011 survey. Enrichment of DOM humic signal (C1, C2, and C4) in brine‐rich (fSIM &lt; 0) waters relative to sea ice melt‐dominated waters (fSIM &gt; 0; p &lt; 0.05) was found during 2011 and 2012 in the offshore region (&gt;76°N) where coastal influences were minimal (fMW &lt; 0.1). Similar fSIM &lt; 0 were found for 2011 and 2012, either when considering the Canada Basin as a whole or the offshore region (&gt;76°N) exclusively, which could imply that brine formation influenced humic signals in polar mixed layer seawater. Findings herein highlight that future projected changes in freshwater sources and brine production in the Canada Basin will likely implicate the distribution and composition of DOM.

On the Origin of Water Masses in the Beaufort Gyre

AbstractThe Beaufort Gyre is a key feature of the Arctic Ocean, acting as a reservoir for freshwater in the region. Depending on whether the prevailing atmospheric circulation in the Arctic is anticyclonic or cyclonic, either a net accumulation or release of freshwater occurs. The sources of freshwater to the Arctic Ocean are well established and include contributions from the North American and Eurasian Rivers, the Bering Strait Pacific water inflow, sea ice meltwater, and precipitation, but their contribution to the Beaufort Gyre freshwater accumulation varies with changes in the atmospheric circulation. Here we use a Lagrangian backward tracking technique in conjunction with the 1/12‐degree resolution Nucleus for European Modelling of the Ocean model to investigate how sources of freshwater to the Beaufort Gyre have changed in recent decades, focusing on increase in the Pacific water content in the gyre between the late 1980s and early 2000s. Using empirical orthogonal functions we analyze the change in the Arctic oceanic circulation that occurred between the 1980s and 2000s. We highlight a “waiting room” advective pathway that was present in the 1980s and provide evidence that this pathway was caused by a shift in the center of Ekman transport convergence in the Arctic. We discuss the role of these changes as a contributing factor to changes in the stratification, and hence potentially the biology, of the Beaufort Gyre region.

North Atlantic and sub-Antarctic Ocean temperatures: possible onset of a transient stadial cooling stage

The ice core glacial-interglacial record of the last 450 kyr (Cortese et al. Paleogeogr Paleoclimatol 22:4, 2007), development of cold ice meltwater regions at fringes of the Greenland and the West Antarctic ice sheets, and climate projections by Hansen et al. (Atmos Chem Phys 16:3761–3812, 2016), support a relation between ice sheet melting and the cooling of neighboring ocean zones by ice meltwater. Several factors lead to cooling of parts of the North Atlantic Ocean and adjacent lands, including the following: (A) a slowdown of the Atlantic meridional overturning circulation (AMOC); (B) flow of cold ice meltwater from the Greenland ice sheet into the North Atlantic Ocean; (C) undulation and weakening of the jet stream at the Arctic boundary due to a rise in temperature in the Arctic circle at twice the rate of warming at lower latitudes and the ice-water albedo flip. Penetration of Arctic-derived cold air masses southward through a weakened jet stream boundary ensues in extreme weather events in North America and Europe. The slowdown of the AMOC (Caesar et al. Nature 556:191–196, 2018; Praetorius Nat Clim Chang 5:475–480, 2018; Thornalley et al. Nature 556:227–230, 2018; Smeed et al. Geophys Res Lett 45(3):1527–1533, 2018) and growing cold ocean region (Rahmstorf et al. Nat Clim Chang 5:475–480, 2015) may herald the onset of a stadial event. A large-scale stadial event, possibly on the scale of the 8.3–8.2 kyr-old Laurentian melt event, or even the 12.9–11.7-kyr-old Younger Dryas stadial (Carlson Encycl Quat Sci 3:126–134, 2013), could ensue from advanced melting of both the Greenland ice sheet and the Antarctic ice sheet. A stadial would be succeeded by the resumption of warming driven by a continuing rise in greenhouse gas concentrations and amplifying feedback effects. These projections need to be examined vis-a-vis the continuous linear IPCC temperature rise models.

Tracing Dissolved Lead Sources in the Canadian Arctic: Insights from the Canadian GEOTRACES Program

This study addresses an important knowledge gap in the distribution of lead (Pb) in the Arctic Ocean, by presenting dissolved Pb concentrations from samples collected during the GEOTRACES Canadian cruise in 2015. Dissolved Pb showed an increase in concentration from the Canada Basin toward Baffin Bay and the Labrador Sea. Canada Basin was the most isolated region from anthropogenic Pb inputs with low background concentrations (1.4–6.2 pmol kg–1) across most of the basin, although higher Pb features from the advection of Pacific-derived waters and sea ice meltwater were present. Likewise, high-Pb peaks (13.5–26.6 pmol kg–1) along narrow isopycnal surfaces (σθ, 27.4–27.6) in Baffin Bay were attributed to the advection of North Atlantic waters spreading a high-Pb signature into the bay, contrasting with the low values (2.5–7.4 pmol kg–1) present in the mixed layer, Arctic and Baffin Bay deep waters. The Labrador Sea, largely influenced by the recirculation of North Atlantic waters, had the highest Pb concent...

Assessing the Contributions of Atmospheric/Meteoric Water and Sea Ice Meltwater and Their Influences on Geochemical Properties in Estuaries of the Canadian Arctic Archipelago

Salinity and stable oxygen isotope (δ18O) data collected from eight estuaries distributed throughout the Canadian Arctic Archipelago were used to apportion contributions from local meteoric water (MW) and sea ice meltwater (SIM) sources during July and August of 2015 and 2016. The size of the rivers flowing into the estuaries varied by an order of magnitude (in terms of mean annual discharge); however, the inventories of MW were always greater or equal to SIM inventories, indicating that MW was the dominant freshwater source. Residence times of MW generally ranged between 1 and 8 days, with longer times (> 20 days) computed for estuaries in the Somerset Island and Baffin Island regions. Shorter residence times indicate, but do not confirm, that river waters move through the estuaries and proceed offshore relatively quickly. Despite this swift transport, nonconservative behaviors were observed for barium and dissolved organic carbon (DOC). These behaviors were identified via examination of total alkalinity, barium, and DOC concentrations that remained after accounting for contributions from MW and seawater . Remaining concentrations/anomalies that deviated significantly from a linear correlation with SIM were attributed to nonconservative behaviors (e.g., desorption of barium from river-borne particles, remineralization of DOC) or inaccurate assignments of endmember values in the water type analyses. Thus, these anomalies offer a means to better inform water type analyses in the correct assignment of endmember properties that best represent the environment studied.

Sea Ice Meltwater and Circumpolar Deep Water Drive Contrasting Productivity in Three Antarctic Polynyas

AbstractIn the Southern Ocean, polynyas exhibit enhanced rates of primary productivity and represent large seasonal sinks for atmospheric CO2. Three contrasting east Antarctic polynyas were visited in late December to early January 2017: the Dalton, Mertz, and Ninnis polynyas. In the Mertz and Ninnis polynyas, phytoplankton biomass (average of 322 and 354 mg chlorophyll a (Chl a)/m2, respectively) and net community production (5.3 and 4.6 mol C/m2, respectively) were approximately 3 times those measured in the Dalton polynya (average of 122 mg Chl a/m2 and 1.8 mol C/m2). Phytoplankton communities also differed between the polynyas. Diatoms were thriving in the Mertz and Ninnis polynyas but not in the Dalton polynya, where Phaeocystis antarctica dominated. These strong regional differences were explored using physiological, biological, and physical parameters. The most likely drivers of the observed higher productivity in the Mertz and Ninnis were the relatively shallow inflow of iron‐rich modified Circumpolar Deep Water onto the shelf as well as a very large sea ice meltwater contribution. The productivity contrast between the three polynyas could not be explained by (1) the input of glacial meltwater, (2) the presence of Ice Shelf Water, or (3) stratification of the mixed layer. Our results show that physical drivers regulate the productivity of polynyas, suggesting that the response of biological productivity and carbon export to future change will vary among polynyas.

Bio‐optical Properties of Surface Waters in the Atlantic Water Inflow Region off Spitsbergen (Arctic Ocean)

AbstractBio‐optical properties of surface waters were characterized off western and northern Spitsbergen in the summers of 2013, 2014, and 2015. We observed statistically significant year‐to‐year differences in spatial distribution of spectral absorption (a(λ)) and beam attenuation (c(λ)). Highest a(λ) and c(λ) were located in the frontal zone between water masses and co‐varied strongly with chlorophyll a fluorescence. Phytoplankton pigments dominated the absorption budget at 443 nm (50%). The contribution of chromophoric dissolved organic matter to total nonwater absorption was highest at 412 nm (42%), and detrital absorption contributed most at 550 nm (37%). Almost all inherent optical properties, except chromophoric dissolved organic matter, were highly correlated with the chlorophyll a concentration (Chla, R2 &gt; 0.81). Relationships between Chla and the particulate and phytoplankton pigments absorption coefficients at 443 and 676 nm were characterized by significant determination coefficients (R2 &gt; 0.73). The phytoplankton pigments line height absorption aLH(676) was found to be the most reliable optical proxy for determination of Chla, compared to total nonwater absorption, apg(676), and stimulated in situ chlorophyll a fluorescence intensity, IChla. In the presence of sea ice melt the water column was stratified and the vertical distribution of inherent optical properties was characterized by a surface minimum followed by a distinct subsurface maximum, aligned with a subsurface chlorophyll a maximum. We surmise that prevailing regional wind patterns affect sea ice and surface drift in central Fram Strait, and thus the location of sea ice meltwater, which affects the vertical stratification and occurrence of subsurface chlorophyll a maximum.

Analysis of runoff characteristics and contribution rate in Xiying River Basin in the Eastern Qilian Mountains

The impact of climate change on the basin is extensive and long-lasting, which will have a profound impact on the natural ecosystems, water resources, agriculture, and human production and life throughout the basin. An in-depth understanding of the impacts of climate change on watersheds and quantitative assessments will help to scientifically plan and manage water resources and protect the integrity of natural ecosystems. In this paper, temperature, precipitation and potential evapotranspiration data were used to analyze the response of Xiying River runoff to climatic factors in the Qilian Mountains by sliding correlation and wavelet analysis. M-K test and cumulative anomaly (CA) were used to analyze the climatic factors and runoff in the basin and use the pettitt method to test. Finally, the cumulative rate slope change rate comparison method was used to analyze the change of precipitation, potential evapotranspiration and snow-melt water contribution to runoff in this area. The results showed that temperature, precipitation and potential evapotranspiration had obvious mutations from 1961 to 2012 in this region. Compared with temperature and potential evapotranspiration, the precipitation showed greater impact on runoff. In addition, the contribution rate of ice and snow melt water to runoff was relatively larger in 1990 - 2002 compared to 1961-1989, followed by precipitation and evapotranspiration; the increase of the precipitation contribution rate became the main factor to runoff, followed by ice and snow melting and evapotranspiration compared to 1990-2002 in 2003-2017.

Recent Sea Ice Decline Did Not Significantly Increase the Total Liquid Freshwater Content of the Arctic Ocean

Abstract The freshwater stored in the Arctic Ocean is an important component of the global climate system. Currently the Arctic liquid freshwater content (FWC) has reached a record high since the beginning of the last century. In this study we use numerical simulations to investigate the impact of sea ice decline on the Arctic liquid FWC and its spatial distribution. The global unstructured-mesh ocean general circulation model Finite Element Sea Ice–Ocean Model (FESOM) with 4.5-km horizontal resolution in the Arctic region is applied. The simulations show that sea ice decline increases the FWC by freshening the ocean through sea ice meltwater and modifies upper ocean circulation at the same time. The two effects together significantly increase the freshwater stored in the Amerasian basin and reduce its amount in the Eurasian basin. The salinification of the upper Eurasian basin is mainly caused by the reduction in the proportion of Pacific Water and the increase in that of Atlantic Water (AW). Consequently, the sea ice decline did not significantly contribute to the observed rapid increase in the Arctic total liquid FWC. However, the changes in the Arctic freshwater spatial distribution indicate that the influence of sea ice decline on the ocean environment is remarkable. Sea ice decline increases the amount of Barents Sea branch AW in the upper Arctic Ocean, thus reducing its supply to the deeper Arctic layers. This study suggests that all the dynamical processes sensitive to sea ice decline should be taken into account when understanding and predicting Arctic changes.

Aqueous alteration of porous microchondrules in Semarkona: Implications for hydration, oxidation and elemental exchange processes

Porous, igneous glassy microchondrules are relatively common in Semarkona and other unequilibrated ordinary chondrites (UOC), occurring embedded within the fine-grained matrices and the chondrule rims. We have investigated the effects of aqueous alteration on two porous microchondrules and associated amorphous silicate materials in the fine-grained matrix of the Semarkona (LL3.00) ordinary chondrite. The iron valency was measured by synchrotron-based scanning transmission X-ray microscopy (STXM) and detailed compositional and mineralogical data were obtained by transmission electron microscopy (TEM). Our STXM data show that the iron in both microchondrules and the amorphous matrix materials is highly oxidized, with elevated ferric iron contents (up to Fe3+/∑Fe ratio 81%). The oxidation process appears to be the result of the interaction of aqueous fluids produced by melting of water ice that accreted into the LL chondrite parent body. The lack of secondary phases such as phyllosilicates or FeO-rich olivines in the microchondrules and the surrounding fine-grained matrix indicates that aqueous alteration was extremely limited. The distribution of major and minor elements indicates limited elemental exchange between the porous microchondrules and the adjacent fine-grained matrix, suggesting that the chemical composition of the two porous microchondrules was not extensively modified during the aqueous alteration. Therefore, these results strongly support the recent conclusions that porous and nonporous microchondrules have different precursor compositions, since their bulk compositions are different and have not been extensively modified by secondary processes.

Winter iron supply processes fueling spring phytoplankton growth in a sub-polar marginal sea, the Sea of Okhotsk: Importance of sea ice and the East Sakhalin Current

To evaluate the winter iron (Fe) supply processes fueling spring phytoplankton growth in the southern Sea of Okhotsk, the distributions of the Fe concentrations in seawater were investigated using hydrographic observations in late November (in the absence of sea ice) and mid-February (in the presence of sea ice). The results obtained from the hydrographic observations indicated a temporal increase in the Fe concentration in the surface mixed layer from November to February, which coincided with a decrease in seawater salinity. Changes in the alkalinity and oxygen isotopic composition of seawater indicated that the mixed layer in February was affected by sea ice meltwater as well as the less saline East Sakhalin Current (ESC) water, with a significant Fe supply originating from these waters. The magnitude of the Fe supply from these waters is greater than the upward Fe supply from deep water. The sea ice meltwater enriches the Fe in the near-surface water of the mixed layer, whereas the ESC water enriches the Fe at the depth of the mixed layer by the entrainment of sedimentary Fe associated with deep mixing due to Ekman transport. Additionally, the Fe nutritional status of the phytoplankton in the surface water of the ice-covered area was investigated by a shipboard incubation experiment. The results showed that bio-available Fe existed in the surface water and that large (>10 μm) phytoplankton were not stressed by low Fe availability. The Fe supply processes related to sea ice melting and the ESC water inflow play important roles in sustaining the suitable Fe nutritional status of phytoplankton in the southern Sea of Okhotsk in early spring.

Sediment composition and its effect on the productivity in Larsemann Hills, East Antarctica

The sediment cores collected from lakes L-8, L-10, and L-12 of Larsemann Hills, East Antarctica, were investigated for sediment components (sand, silt, clay, total organic carbon, total nitrogen, total phosphorus, elemental TOC/TN ratio, and biogenic silica or biogenic opal), major elements (Al, Fe, Mn, Ti, Mg, Ca), and trace metals (Cr, Co, Zn, Cd, Pb, Ba, Cu, Ni) to understand the source, processes, and productivity in the lacustrine sediments. In lake L-10, average sand content was higher than in lakes L-8 and L-12 which indicated the high intensity of mechanical weathering, resulted in releasing coarse-grained material from the rocks in the catchment area. High Ti/Al molar ratios (2.00–3.32) in all the three cores resulted from shorter transportation distance from different parent sources. Higher clay content near the surface in all the three lakes indicated deposition of fine-grained particles supplied by ice-melt water owing to ice-free conditions in the area in recent years. Relatively, higher biogenic silica along with high total organic carbon associated with high clay in the upper section of lakes L-10 and L-12 and middle section of core L-8 indicated deposition of finer particles from suspension which facilitated high primary productivity due to exposure of the lakes to the ice-melt water influx. Further, Mg/Ca ratio in all the three lakes was high near the surface indicating enrichment of biogenic sedimentation. C/N ratio was found to be much less than 10, indicating the major source of organic matter is autochthonous and exclusively derived from algae (C/N < 10) in all the cores. The metal concentration was found to be higher in core L-8 and was found to be associated with finer sediments, as compared to cores L-10 and L-12 where coarser sediments must have diluted the metal content. Ba was found to be of biogenic origin in cores L-8 and L-12 while in core L-10 it was of lithogenic origin. Cd, Zn, and Ni in all the three lakes were found to be mainly of biogenic origin, whereas all other metals studied were of lithogenic origin. Thus, the concentration of trace metals in Larsemann Hill lake sediments is entirely by natural processes regulated by lithology, catchment processes, and climatic conditions.

Characteristics of chromophoric and fluorescent dissolved organic matter in the Nordic Seas

Abstract. Optical properties of chromophoric (CDOM) and fluorescent dissolved organic matter (FDOM) were characterized in the Nordic Seas including the West Spitsbergen Shelf during June–July 2013, 2014, and 2015. The CDOM absorption coefficient at 350 nm, aCDOM(350) showed significant interannual variation (T test, p &lt; 0.00001). In 2013, the highest average aCDOM(350) values (aCDOM(350) = 0.30 ± 0.12 m−1) were observed due to the influence of cold and low-salinity water from the Sørkapp Current (SC) in the southern part of the West Spitsbergen Shelf. In 2014, aCDOM(350) values were significantly lower (T test, p &lt; 0.00001) than in 2013 (average aCDOM(350) = 0.14 ± 0.06 m−1), which was associated with the dominance of warm and saline Atlantic Water (AW) in the region, while in 2015 intermediate CDOM absorption (average aCDOM(350) = 0.19 ± 0.05 m−1) was observed. In situ measurements of three FDOM components revealed that fluorescence intensity of protein-like FDOM dominated in the surface layer of the Nordic Seas. Concentrations of marine and terrestrial humic-like DOM were very low and distribution of those components was generally vertically homogenous in the upper ocean (0–100 m). Fluorescence of terrestrial and marine humic-like DOM decreased in surface waters (0–15 m) near the sea ice edge due to dilution of oceanic waters by sea ice meltwater. The vertical distribution of protein-like FDOM was characterized by a prominent subsurface maximum that matched the subsurface chlorophyll a maximum and was observed across the study area. The highest protein-like FDOM fluorescence was observed in the Norwegian Sea in the core of warm AW. There was a significant relationship between the protein-like fluorescence and chlorophyll a fluorescence (R2 = 0.65, p &lt; 0.0001, n = 24 490), which suggests that phytoplankton was the primary source of protein-like DOM in the Nordic Seas and West Spitsbergen Shelf waters. Observed variability in selected spectral indices (spectral slope coefficient, S300–600, carbon-specific CDOM absorption coefficient at 254 and 350 nm, SUVA254, aCDOM*(350)) and the nonlinear relationship between CDOM absorption and the spectral slope coefficient also indicate a dominant marine (autochthonous) source of CDOM and FDOM in the study area. Further, our data suggest that aCDOM(350) cannot be used to predict dissolved organic carbon (DOC) concentrations in the study region; however the slope coefficient (S300–600) shows some promise in being used.

Use of palmitoleic acid and its oxidation products for monitoring the degradation of ice algae in Arctic waters and bottom sediments

Degradation of palmitoleic acid (C16:1ω7), the main fatty acid component of sea ice-associated (sympagic) diatoms, was monitored in Arctic sea ice at the beginning of ice melting and in the underlying sinking particles and superficial bottom sediments. In sea ice, degradation of sympagic algae involved biotic oxidation induced by 10S-DOX-like lipoxygenase of unknown salinity-stressed attached bacteria, while photo- and autoxidation were limited. In the water column, strong hydratase and Z/E isomerase activity were observed. Hydration of unsaturated fatty acids seems to be a detoxification strategy, which is essential for bacterial survival when associated with free fatty acid-rich environments such as ice algae. In contrast, Z/E isomerisation of palmitoleic acid was attributed to the release of Fe2+ ions during radical-induced damage of the active site of the bacterial 10S-DOX-like lipoxygenase and Z/E isomerases. Due to the poor physiological state of their attached bacteria resulting from salinity stress in brine channels or toxicity of free ice algae fatty acids, sympagic algae appeared to be only very weakly biotically degraded within the water column. In bottom sediments, free radicals resulting from 10S-DOX-like lipoxygenase activity induced a strong autoxidation of the ice algal material. The presence in bottom sediments of a significant proportion of oxidation products resulting from 10S-DOX-like lipoxygenase activity attested to the strong contribution of sea ice-derived OM released during the early stages of ice melt prior to deposition in the sediments. However, on the basis of the highest fatty acid photooxidation state observed in these sediments, an additional contribution of highly photooxidized material (ice algal material released at the end of ice melting or open water phytoplankton) seems likely. The degradation of hydroperoxides, resulting from biotic and abiotic degradation of palmitoleic acid, appeared to involve: (i) homolytic cleavage of the peroxyl group affording the corresponding hydroxy- and oxoacids, (ii) reduction to the corresponding hydroxyacids by peroxygenases, (iii) heterolytic proton-catalysed cleavage and (iv) conversion to allylic 1,4-diols by diol synthases and hydroperoxide isomerases.