Arctic Ocean Surface Waters Research Articles

Concentrations of dissolved dimethyl sulfide (DMS), methanethiol and other trace gases in context of microbial communities from the temperate Atlantic to the Arctic Ocean

Abstract. Dimethyl sulfide (DMS) plays an important role in the atmosphere by influencing the formation of aerosols and cloud condensation nuclei. In contrast, the role of methanethiol (MeSH) for the budget and flux of reduced sulfur remains poorly understood. In the present study, we quantified DMS and MeSH together with the trace gases carbon monoxide (CO), isoprene, acetone, acetaldehyde and acetonitrile in North Atlantic and Arctic Ocean surface waters, covering a transect from 57.2 to 80.9∘ N in high spatial resolution in May–June 2015. Whereas isoprene, acetone, acetaldehyde and acetonitrile concentrations decreased northwards, CO, DMS and MeSH retained substantial concentrations at high latitudes, indicating specific sources in polar waters. DMS was the only compound with a higher average concentration in polar (31.2 ± 9.3 nM) than in Atlantic waters (13.5 ± 2 nM), presumably due to DMS originating from sea ice. At eight sea-ice stations north of 80∘ N, in the diatom-dominated marginal ice zone, DMS and chlorophyll a markedly correlated (R2 = 0.93) between 0–50 m depth. In contrast to previous studies, MeSH and DMS did not co-vary, indicating decoupled processes of production and conversion. The contribution of MeSH to the sulfur budget (represented by DMS + MeSH) was on average 20 % (and up to 50 %) higher than previously observed in the Atlantic and Pacific oceans, suggesting MeSH as an important source of sulfur possibly emitted to the atmosphere. The potential importance of MeSH was underlined by several correlations with bacterial taxa, including typical phytoplankton associates from the Rhodobacteraceae and Flavobacteriaceae families. Furthermore, the correlation of isoprene and chlorophyll a with Alcanivorax indicated a specific relationship with isoprene-producing phytoplankton. Overall, the demonstrated latitudinal and vertical patterns contribute to understanding how concentrations of central marine trace gases are linked with chemical and biological dynamics across oceanic waters.

Element transport in the Taz River, western Siberia

The riverine export fluxes of dissolved carbon, nutrient and metals from the land to the Arctic Ocean are fairly well quantified for five large Arctic rivers but remain virtually unknown for mid-sized Eurasian rivers, notably those draining through the permafrost zone. Because such rivers can most rapidly respond to on-going climate warming and permafrost thaw in the Arctic, their current hydrochemical composition and elemental yields are badly needed for judging the level of changes in the very near future. Towards quantifying the annual export fluxes and assessing the mechanisms of seasonal variability of river solutes, we monitored the pristine subarctic Taz River (Swatershed = 150,000 km2), which drains through boreal forest and peatlands in the discontinuous and continuous permafrost zone, on a weekly to monthly basis over a 3 year period.Based on seasonal pattern of riverine solutes (< 0.45 μm) and their dependence on discharge, 3 groups of elements were distinguished. These groups of solutes were consistent with several main sources of elements in the main stem of the Taz River such as deep groundwater, riparian zone and floodplain lake sediments, plant litter, mineral soil water, and peatwater from the peatlands. The 1st group was represented by dissolved inorganic carbon (DIC), specific conductivity, and some nutrients (NO3, NH4, Ntot and Si) and soluble elements that originated from groundwater and deep soil mineral horizons (Cl, SO4, Li, B, Na, Mg, Ca, Si, K, Rb, Mn, Co, Sr, Mo, Cs, Ba and W) and showed maximal concentration at the end of winter, before the spring ice-off. This group showed negative correlation to discharge. The 2nd group included dissolved organic carbon (DOC), low-mobile hydrolysates and organically-complexed trace metals (Al, Be, V, Ni, Y, Se, Zr, Nb, REEs, Hf, Pb and Th) which demonstrated maximal concentrations during the spring flood and autumn high flow and minimal values during winter. The concentration of these elements generally increased with water discharge, presumably due to their mobilization in the form of organic and organo-mineral colloids by surface flow through forest litter and via suprapermafrost flow from peatlands. And lastly, the 3rd group of solutes included macronutrients (P, N), Fe, Ti, Cr, Ga, Ge, As, Pb, and U which exhibited features of first two groups and originated from both surface and underground sources. This group showed the strong impact of autochthonous biotic processes in the river channel and soils of the watershed (nutrients, Si).Similar to other Arctic rivers, the spring flood (May and June) provided 30–40% of annual export for DOC, macronutrients and most major and minor solutes. The exceptions are DIC, Si, Ca, Mg and Fe which exhibited essential (30–40%) export during winter baseflow, whereas >70% of annual Mn flux occurred in winter. A number of elements present in the snowpack exhibited sizable (> 45%) export during spring flood (Zn, Cu, Pb, Cd, Sb and Cs). The 3 years mean export fluxes (yields) of dissolved components were comparable to or 30–50% lower than those of other large and medium sized Arctic rivers. This was due mostly to a lack of fresh unaltered rocks and a dominance of peatlands within the Taz River watershed. Elevated concentrations of redox-sensitive micro-nutrients (such as Fe and Mn) occurring during winter baseflow can be linked to disproportionally large floodplain zone of this river which can act, especially in the river's lower reaches, as a stratified lake thereby releasing high amounts of redox-sensitive elements from the sediments. The role of suboxic zones in the Arctic boreal riverine landscape may be more important than previously thought, and may allow explaining anomalously high concentrations of some metals (i.e., Mn) reported in Arctic Ocean surface waters. It is anticipated that climate warming in the region may increase the contribution of winter flow and enhance the export of soluble elements and some nutrients (such as Si, Mn and Co).

Arctic Ocean annual high in {{boldsymbol{p}}}_{{{bf{CO}}}_{{bf{2}}}} could shift from winter to summer

Long-term stress on marine organisms from ocean acidification will differ between seasons. As atmospheric carbon dioxide (CO2) increases, so do seasonal variations of ocean CO2 partial pressure ({p}_{{{rm{CO}}}_{2}}), causing summer and winter long-term trends to diverge1–5. Trends may be further influenced by an unexplored factor—changes in the seasonal timing of {p}_{{{rm{CO}}}_{2}}. In Arctic Ocean surface waters, the observed timing is typified by a winter high and summer low6 because biological effects dominate thermal effects. Here we show that 27 Earth system models simulate similar timing under historical forcing but generally project that the summer low, relative to the annual mean, eventually becomes a high across much of the Arctic Ocean under mid-to-high-level CO2 emissions scenarios. Often the greater increase in summer {p}_{{{rm{CO}}}_{2}}, although gradual, abruptly inverses the chronological order of the annual high and low, a phenomenon not previously seen in climate-related variables. The main cause is the large summer sea surface warming7 from earlier retreat of seasonal sea ice8. Warming and changes in other drivers enhance this century’s increase in extreme summer {p}_{{{rm{CO}}}_{2}} by 29 ± 9 per cent compared with no change in driver seasonalities. Thus the timing change worsens summer ocean acidification, which in turn may lower the tolerance of endemic marine organisms to increasing summer temperatures.

Photochemical Degradation of Dimethylmercury in Natural Waters.

Photochemical demethylation of dimethylmercury (DMHg) could potentially be an important source of monomethylmercury (MMHg) in sunlit water. Whether or not DMHg is photochemically degraded when dissolved in water is, however, debated. While an early study suggested DMHg dissolved in natural waters to readily degrade, later work claimed DMHg to be stable in seawater under natural sunlight and that early observations may be due to experimental artifacts. Here, we present experimental data showing that DMHg is readily degraded by photochemical processes in different natural waters (including water from a DOC-rich stream, the Baltic Sea, and the Arctic Ocean) as well as in artificial seawater and purified water. For most of the waters, the degradation rate constant (kd) for DMHg measured in indoor experiments exceeded, or was close to, the kd observed for MMHg. Outdoor incubations of DMHg in purified water and Arctic Ocean surface water further confirmed that DMHg is photochemically degraded under natural sunlight. Our study shows that DMHg is photochemically degraded in a range of natural waters and that this process may be a source of MMHg in sunlit waters where the supply or formation of DMHg is sufficient.

Compositional differences of fluorescent dissolved organic matter in Arctic Ocean spring sea ice and surface waters north of Svalbard

We assessed the qualitative composition of fluorescent dissolved organic matter (FDOM) in Arctic Ocean surface water and in sea ice north of the Svalbard Archipelago (in the Sophia Basin, the Yermak Plateau and the north Spitsbergen shelf) in May and June 2015, during the “TRANSSIZ” expedition (Transitions in the Arctic Seasonal Sea Ice Zone). Samples collected in open lead waters (OW), under-ice waters (UIW) and from the sea ice (ICE) were analyzed by fluorescence spectroscopy and subsequently by multivariate statistical methods using Parallel Factor Analysis (PARAFAC). Statistical analyses of all measured DOM fluorescence excitation and emission matrices (EEMs) enabled four components to be identified and validated. The spectral characteristics of the first component C1 (λEx/λEm 282(270)/335) corresponded to those of tryptophan. The spectral properties of the other three components corresponded to those of humic-like substances: components two (C2 − λEx/λEm 315(252)/395) and three (C3 − λEx/λEm 357(258)/446) corresponded to humic-like substances of marine origin, whereas component four (C4 − λEx/λEm 261(399)/492) resembled terrestrial humic-like substances. Changes in FDOM composition were recorded in OW, in contrast to UIW and sea ice. In the OW the sum of fluorescence intensities of humic-like components (C2, C3 and C4) was two times higher than the fluorescence intensity of protein-like component (C1). Component C2 exhibited the highest fluorescence intensity. In the UIW and particularly in the sea ice the fluorescence intensity of the protein-like component, IC1, was the highest. The IC1 in the sea ice increased toward the sea ice bottom, reaching maximum values at the sea ice-water interface. The calculated spectral indices (SUVA(254) and HIX) and ratios of fluorescence intensities of protein-like to humic-like components, Ip/Ih, suggested that FDOM in water and sea ice was predominantly autochthonous, characterized by low molecular weight organic compounds and low aromatic ring saturation. Enrichment factors Dc, calculated from salinity-normalized values of the optical DOM properties and dissolved organic carbon concentrations, indicated the significant fractionation of FDOM in the sea ice relative to the parent open waters. The humic-like terrestrial component C4 was enriched the least, whereas the protein-like component C1 was enriched the most. A statistically significant (p < 0.0001) and relatively strong (R = 63) correlation between IC1 and the total chlorophyll a concentration Tchla was found in the sea ice, which suggests that sympagic algal communities were producers of the protein-like FDOM fraction.

Emergent constraint on Arctic Ocean acidification in the twenty-first century.

The ongoing uptake of anthropogenic carbon by the ocean leads to ocean acidification, a process that results in a reduction in pH and in the saturation state of biogenic calcium carbonate minerals aragonite (Ωarag) and calcite (Ωcalc)1,2. Because of its naturally low Ωarag and Ωcalc (refs. 2,3), the Arctic Ocean is considered the region most susceptible to future acidification and associated ecosystem impacts4-7. However, the magnitude of projected twenty-first century acidification differs strongly across Earth system models8. Here we identify an emergent multi-model relationship between the simulated present-day density of Arctic Ocean surface waters, used as a proxy for Arctic deep-water formation, and projections of the anthropogenic carbon inventory and coincident acidification. By applying observations of sea surface density, we constrain the end of twenty-first century Arctic Ocean anthropogenic carbon inventory to 9.0±1.6 petagrams of carbon and the basin-averaged Ωarag and Ωcalc to 0.76±0.06 and 1.19±0.09, respectively, under the high-emissions Representative Concentration Pathway 8.5 climate scenario. Our results indicate greater regional anthropogenic carbon storage and ocean acidification than previously projected3,8 and increase the probability that large parts of the mesopelagic Arctic Ocean will be undersaturated with respect to calcite by the end of the century. This increased rate of Arctic Ocean acidification, combined with rapidly changing physical and biogeochemical Arctic conditions9-11, is likely to exacerbate the impact of climate change on vulnerable Arctic marine ecosystems.

Concentrations, provenance and flux of aerosol trace elements during US GEOTRACES Western Arctic cruise GN01

The Arctic region is undergoing significant changes in climate, with a notable decrease in summertime sea ice coverage over the past three decades. This trend means an increasing proportion of Arctic Ocean surface waters can receive direct deposition of material from the atmosphere, potentially influencing marine biogeochemical cycles and delivery of pollutants to the Arctic ecosystem. Here, we present aerosol concentrations of selected trace elements (Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) measured during the US GEOTRACES Western Arctic cruise (GN01, also known as HLY1502) in August–October 2015. Concentrations of “lithogenic” elements (Al, Ti, V, Mn, Fe, and Co) were similar to those measured in remote and predominantly marine-influenced air masses in previous studies, reflecting the remoteness of the Arctic Ocean from major dust sources. Concentrations of Ni, Cu, Zn, Pb, and Cd showed significant enrichments over crustal values, and were often of similar magnitude to concentrations measured over the North Atlantic in air masses of North American or European provenance. We use 7Be inventory and flux data from GN01 to estimate a bulk atmospheric deposition velocity during the study period, and combine it with our aerosol concentrations to calculate atmospheric deposition fluxes of the trace elements in the Arctic region during late summer. The resulting estimates for mineral dust and Fe deposition fall at the low end of global estimates and confirm the Arctic Ocean as a low-dust environment during the summer months.This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

High colored dissolved organic matter (CDOM) absorption in surface waters of the central-eastern Arctic Ocean: Implications for biogeochemistry and ocean color algorithms.

As consequences of global warming sea-ice shrinking, permafrost thawing and changes in fresh water and terrestrial material export have already been reported in the Arctic environment. These processes impact light penetration and primary production. To reach a better understanding of the current status and to provide accurate forecasts Arctic biogeochemical and physical parameters need to be extensively monitored. In this sense, bio-optical properties are useful to be measured due to the applicability of optical instrumentation to autonomous platforms, including satellites. This study characterizes the non-water absorbers and their coupling to hydrographic conditions in the poorly sampled surface waters of the central and eastern Arctic Ocean. Over the entire sampled area colored dissolved organic matter (CDOM) dominates the light absorption in surface waters. The distribution of CDOM, phytoplankton and non-algal particles absorption reproduces the hydrographic variability in this region of the Arctic Ocean which suggests a subdivision into five major bio-optical provinces: Laptev Sea Shelf, Laptev Sea, Central Arctic/Transpolar Drift, Beaufort Gyre and Eurasian/Nansen Basin. Evaluating ocean color algorithms commonly applied in the Arctic Ocean shows that global and regionally tuned empirical algorithms provide poor chlorophyll-a (Chl-a) estimates. The semi-analytical algorithms Generalized Inherent Optical Property model (GIOP) and Garver-Siegel-Maritorena (GSM), on the other hand, provide robust estimates of Chl-a and absorption of colored matter. Applying GSM with modifications proposed for the western Arctic Ocean produced reliable information on the absorption by colored matter, and specifically by CDOM. These findings highlight that only semi-analytical ocean color algorithms are able to identify with low uncertainty the distribution of the different optical water constituents in these high CDOM absorbing waters. In addition, a clustering of the Arctic Ocean into bio-optical provinces will help to develop and then select province-specific ocean color algorithms.

The Air-Sea Nitrous Oxide Flux along Cruise Tracks to the Arctic Ocean and Southern Ocean

Nitrous oxide is a trace gas with two global environmental effects: it depletes stratospheric ozone and contributes to the greenhouse effect. Oceans are one of the most significant nitrous oxide sources; however, there are ocean areas whose contributions to the nitrous oxide budget are not yet well studied. The Southern Ocean and the Arctic Ocean feature strong winds and portions that are covered by sea ice. These intense environmental conditions and the remoteness of these regions hamper fieldwork; hence, very limited data are available on the distributions and the source and sink characteristics of nitrous oxide. Using data from the 4th Chinese National Arctic Research Expedition and the 27th Chinese National Antarctic Research Expedition, the first global-scale investigation of the surface water N2O distribution pattern, the factors influencing the N2O distribution and the air-sea N2O flux are discussed in this study. The results show that the tropical and subtropical regions (30° N–30° S) exhibit significant source characteristics, with a maximum air-sea flux of approximately 21.0 ± 3.9 μmol·m−2·d−1. The high air-sea flux may result from the coastal influences and high wind speeds in certain areas. The distribution patterns of N2O in the sub-polar regions (30° N–60° N, 30° S–60° S) transition from oversaturated to approximate equilibrium with the atmosphere, and the boundaries generally correspond with frontal structures. The distributions of N2O in the high-latitude Southern Ocean and Arctic Ocean (&gt;60° N and 60° S) exhibit contrasting patterns. With the exception of the continental shelf hotspot, the Arctic Ocean surface water is undersaturated with N2O; in contrast, the high-latitude Southern Ocean along the cruise track is oversaturated with N2O. The high-latitude Southern Ocean may act as a N2O source, with a maximum air-sea N2O flux of approximately 9.8 ± 0.5 μmol·m−2·d−1 at approximately 60° S, whereas the air-sea N2O flux of the Arctic Ocean is close to zero due to the low wind speed conditions at these latitudes.

Response of phytoplankton community to different water types in the western Arctic Ocean surface water based on pigment analysis in summer 2008

Nutrients and photosynthesis pigments were investigated in the western Arctic Ocean during the 3rd Chinese Arctic Research Expedition Cruise in summer 2008. The study area was divided into five provinces using the Kmeans clustering method based on the physical and chemical characteristics of the sea water, and to discuss the distribution of the phytoplankton community structure in these provinces. CHEMTAX software was performed using HPLC pigments to estimate the contributions of eight algal classes to the total chlorophyll a (TChl a). The results showed that on the Chukchi Shelf, the Pacific Ocean inflow mainly controlled the Chl a biomass and phytoplankton communities by nutrient concentrations. The high nutrient Anadyr Water and Bering Shelf Water (AnW and BSW) controlled region have high Chl a levels and the diatom dominated community structure. In contrast, in the region occupied by low-nutrient like Alaska Coastal Water (ACW), the Chl a biomass was low, with pico- and nano-phytoplankton as dominated species, such as prasinophytes, chrysophytes and cryptophytes. However, over the off-shelf, the ice cover condition which would affect the physical and nutrient concentrations of the water masses, in consequence had a greater impact on the phytoplankton community structure. Diatom dominated in ice cover region and its contribution to Chl a biomass was up to 75%. In the region close to the Mendeleev Abyssal Plain (MAP), controlled by sea-ice melt water with relatively high salinity (MW-HS), higher nutrient and Chl a concentrations were found and the phytoplankton was dominated by pico- and nano-algae, while the diatom abundance reduced to 33%. In the southern Canada Basin, an ice-free basin (IfB) with the lowest nutrient concentrations and most freshened surface water, low Chl a biomass was a consequence of low nutrients. The ice retreating and a prolonged period of open ocean may not be beneficial to the carbon export efficiency due to reducing the Chl a biomass or intriguing smaller size algae growth.

Diazotroph Diversity in the Sea Ice, Melt Ponds, and Surface Waters of the Eurasian Basin of the Central Arctic Ocean.

The Eurasian basin of the Central Arctic Ocean is nitrogen limited, but little is known about the presence and role of nitrogen-fixing bacteria. Recent studies have indicated the occurrence of diazotrophs in Arctic coastal waters potentially of riverine origin. Here, we investigated the presence of diazotrophs in ice and surface waters of the Central Arctic Ocean in the summer of 2012. We identified diverse communities of putative diazotrophs through targeted analysis of the nifH gene, which encodes the iron protein of the nitrogenase enzyme. We amplified 529 nifH sequences from 26 samples of Arctic melt ponds, sea ice and surface waters. These sequences resolved into 43 clusters at 92% amino acid sequence identity, most of which were non-cyanobacterial phylotypes from sea ice and water samples. One cyanobacterial phylotype related to Nodularia sp. was retrieved from sea ice, suggesting that this important functional group is rare in the Central Arctic Ocean. The diazotrophic community in sea-ice environments appear distinct from other cold-adapted diazotrophic communities, such as those present in the coastal Canadian Arctic, the Arctic tundra and glacial Antarctic lakes. Molecular fingerprinting of nifH and the intergenic spacer region of the rRNA operon revealed differences between the communities from river-influenced Laptev Sea waters and those from ice-related environments pointing toward a marine origin for sea-ice diazotrophs. Our results provide the first record of diazotrophs in the Central Arctic and suggest that microbial nitrogen fixation may occur north of 77°N. To assess the significance of nitrogen fixation for the nitrogen budget of the Arctic Ocean and to identify the active nitrogen fixers, further biogeochemical and molecular biological studies are needed.

A hypothesis on variability of surface water &amp;lt;italic&amp;gt;p&amp;lt;/italic&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; under the rapid sea-ice retreat during summer in the Arctic Ocean

The Arctic Ocean has been recognized to play an active role in global carbon cycle due to its potential to disproportionally take up CO2 from the atmosphere especially under a dwindling ice extent. It is estimated that the Arctic Ocean will be responsible for up to 5%–14% of the total global oceanic CO2 uptake even though it comprises only 3% of the world ocean surface area. Over the past decade, the sea ice in the Arctic Ocean has significantly retreated during summer. The rapid sea ice retreat is thought to cause corresponding changes in the distribution of p CO2 in the surface waters of Arctic Ocean. However, the response of carbon dynamics to a changing Arctic Ocean remains poorly quantified. It has been postulated that an ice-free condition in the Arctic Ocean basins would allow for uptake of a substantial amount of carbon dioxide (CO2) from the atmosphere as a result of sea ice melt and increasing primary productivity. However, the other direct observation-based study of high-resolution survey of sea-surface CO2 concentration across the Canada Basin, showing a great high p CO2 relative to earlier observations and predicted that the Arctic Ocean basin will not become a large atmospheric CO2 sink under ice-free conditions. Due to the existing quite different views, thus, there is an implication of observation-based learning in the variations of the surface seawater p CO2 under a scenario of rapid sea ice melting. In the summer of 2008, during the 3rd Chinese National Arctic Research Expedition (CHINARE) cruise, significant variability of p CO2 in surface water has been observed along a trans-Arctic section of 150°–160°W from the Chukchi Sea slope to 88°N in the western Arctic Ocean. We propose a hypothesis of “low-low-high” variation trend in surface water p CO2 levels along a decreasing ice-cover gradient across three different zones in the Arctic Ocean under a rapid sea ice melting scenario in the summer. Specifically, there are (1) “low” p CO2 levels of ~270–280 μ atm in the sea ice-covered zone (north of 84°N) with a high ice concentration >70%; (2) “low” p CO2 of ~250–270 μ atm in a sea ice melting zone (78°–81°N) with a medium ice extent of around 50%; and (3) “high” p CO2 of ~320–365 μ atm in an ice-free zone (72°–77°N) with a low ice concentration of p CO2 variation trend could be attributed to different driving forces. The low p CO2 in the heavily ice-covered northern basin is likely influenced by a combination of several processes, including mixing of various source waters, CO2 fixation by ice algae, ice-water gas exchange, and temperature change, although their relative roles remain to be quantified. The low p CO2 observed in the partially ice-covered northern Canada Basin could be primarily derived from biological CO2 fixation and the dissolution of CaCO3 precipitates, both of which consume CO2. Primary productivity enhanced by the early melting of sea ice plays an important role in the decreased sea-surface p CO2. In addition, sea ice melting also promotes the dissolution of authigenic CaCO3 in the form of ikaite within the sea ice. Finally, results of tracer data and model simulations suggest that the rapid CO2 invasion from the atmosphere and low biological export of CO2 owing to a shallow mixed-layer depth, strong subsurface water stratification, and limited nutrient supply to the surface water are both responsible for the observed high p CO2 values in the ice-free southern Canada Basin.

An 11 000‐year record of driftwood delivery to the western Queen Elizabeth Islands, Arctic Canada

Fifty‐six new radiocarbon dates from driftwood (mainly Larix, Picea and Populus spp.) collected from the modern and raised shorelines of Melville and Eglinton islands (western Canadian High Arctic) are presented and compared to other driftwood collections from the Canadian Arctic Archipelago (CAA) and Greenland. By documenting the species (provenance) and spatio‐temporal distribution of driftwood at various sites across the Arctic, regional characterizations of former sea‐ice conditions and changes in Arctic Ocean circulation patterns may be deduced. The earliest postglacial invasion of the Canadian Arctic Archipelago by driftwood is recorded on central Melville Island at c. 11 cal. ka BP, suggesting that the modern circulation pattern of Arctic Ocean surface water southeast through the archipelago was established &gt;1000 years earlier than previously proposed. Throughout most of the Holocene until c. 1.0 cal. ka BP, the rate of driftwood delivery to the western Arctic islands was low (~1 recorded stranding event per 200 years) and intermittent, with the longest break in the record occurring between c. 3.0 and 5.0 cal. ka BP. This 2000‐year hiatus is attributed to a period of colder temperatures causing severe sea‐ice conditions and effectively making the coasts of the western Arctic islands inaccessible. After c. 1.0 cal. ka BP, driftwood incursion increased to maximum Holocene levels (~1 recorded stranding event every 20 years). Driftwood identified to the genus level as Larix that was delivered at this time suggests that the Trans Polar Drift current was regularly in its most southwestern position, related to a dominantly positive Arctic Oscillation mode. The Little Ice Age appears to have had little impact on driftwood entry to the western Canadian Arctic Archipelago, indeed the general abundance in the latest Holocene may record infrequent landfast sea ice.

Assessing the potential impacts of declining Arctic sea ice cover on the photochemical degradation of dissolved organic matter in the Chukchi and Beaufort Seas

AbstractA warming and shifting climate in the Arctic has led to significant declines in sea ice over the last several decades. Although these changes in sea ice cover are well documented, large uncertainties remain in how associated increases in solar radiation transmitted to the underlying ocean water column will impact heating, biological, and biogeochemical processes in the Arctic Ocean. In this study, six under‐ice marine, two ice‐free marine, and two ice‐free terrestrially influenced water samples were irradiated using a solar simulator for 72 h (representing ~10 days of ambient sunlight) to investigate dissolved organic matter (DOM) dynamics from the Chukchi and Beaufort Seas. Solar irradiation caused chromophoric DOM (CDOM) light absorption at 254 nm to decrease by 48 to 63%. An overall loss in total DOM fluorescence intensity was also observed at the end of all experiments, and each of six components identified by parallel factor (PARAFAC) analysis was shown to be photoreactive in at least one experiment. Fluorescent DOM (FDOM) also indicated that the majority of DOM in under‐ice and ice‐free marine waters was likely algal‐derived. Measurable changes in dissolved organic carbon (DOC) were only observed for sites influenced by riverine runoff. Losses of CDOM absorbance at shorter wavelengths suggest that the beneficial UV protection currently received by marine organisms may decline with the increased light transmittance associated with sea ice melt ponding and overall reductions of sea ice. Our FDOM analyses demonstrate that DOM irrespective of source was susceptible to photobleaching. Additionally, our findings suggest that photodegradation of CDOM in under‐ice waters is not currently a significant source of carbon dioxide (CO2) (i.e., we did not observe systematic DOC loss). However, increases in primary production and terrestrial freshwater export expected under future climate change scenarios may cause an increase in CDOM quantity and shift in quality throughout Arctic Ocean surface waters. As Arctic temperatures continue to warm and summer sea ice further declines, examination of the resulting enhanced photodegradation processes and their impacts on the interplay between primary production, carbon cycling, and surface ocean heating processes will be paramount.

Light absorption and partitioning in Arctic Ocean surface waters: impact of multiyear ice melting

Abstract. Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposition in the upper ocean. In August 2009, we documented the vertical variability of light absorbing components at 37 stations located in the southeastern Beaufort Sea including both Mackenzie River-influenced waters and polar mixed layer waters. We found that melting multiyear ice released significant amount of non-algal particulates (NAP) near the sea surface relative to subsurface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface were on average 3-fold (up to 10-fold) higher compared to subsurface values measured at 2–3 m depth. The impact of this unusual feature on the light transmission and remote sensing reflectance (Rrs) was further examined using a radiative transfer model. A 10-fold particle enrichment homogeneously distributed in the first meter of the water column slightly reduced photosynthetically available and usable radiation (PAR and PUR) by ∼6 and ∼8%, respectively, relative to a fully homogenous water column with low particle concentration. In terms of Rrs, the particle enrichment significantly flattered the spectrum by reducing the Rrs by up to 20% in the blue-green spectral region (400–550 nm). These results highlight the impact of meltwater on the concentration of particles at sea surface, and the need for considering non-uniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV (ultraviolet) domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM (particulate organic matter) photobleaching).

11,000 yrs of environmental change in the Northwest Passage: A multiproxy core record from central Parry Channel, Canadian High Arctic

Abstract Piston core 97022-004PC (74° 48.0′N 97°05.9′W; 267 m water depth) represents a rare paleoenvironmental archive from the understudied west-central Canadian Arctic Archipelago. Lithological, biogeochemical, and microfossil (dinoflagellate cysts, non-pollen palynomorphs, benthic and planktonic foraminifera) characteristics, in combination with a chronostratigraphy based on seventeen radiocarbon dates, show seven prominent paleoenvironmental episodes since the end of the last regional glaciation. The basal diamict (Zone I) records decoupling of previously grounded glacial ice, followed by ice-proximal conditions (Zone IIa) commencing at ~ 10.8 cal ka BP (age-depth model extrapolation). After an interval of pervasive sea-ice (Zone IIb), ice-distal conditions are established (Zone IIc). Although sparse microfossils are present in glaciomarine sediments (Zone II), noticeable biological activity with heightened abundances and diversities across all groups begins in the postglacial Zone III (10.3–10.0 cal ka BP) when planktonic foraminifera (Neogloboquadrina pachyderma) appear. As planktonics are excluded from the study area today (due to shallow inter-channel sills), this likely signals the inflow of relatively warm and saline Atlantic-derived Arctic Intermediate Water below 250 m, presumably facilitated by glacio-isostatically enhanced deglacial water depths. The subsequent Zone IV (10.0–7.0 cal ka BP), characterized by heightened biological productivity in both plankton and benthos and reduced seasonal sea-ice cover, may correspond to a previously proposed Holocene Thermal Maximum. This apparent amelioration ends by the mid Holocene (Zone V; 7.0–5.7 cal ka BP) when Arctic Intermediate Water is excluded from the study area and water depths approach modern values. High-Arctic conditions with seasonal sea-ice cover, a circulation dominated by Arctic Ocean Surface Water, and microfossil assemblages similar to modern are found from ~ 5.7 cal ka BP onwards (Zones VI–VII). As only minor environmental fluctuations are apparent during the late Holocene, shorter-term climatic episodes (e.g. Little Ice Age) are not recognized in this record.

Light absorption and partitioning in Arctic Ocean surface waters: impact of multiyear ice melting

Light absorption and partitioning in Arctic Ocean surface waters: impact of multiyear ice melting

Dissolved organic nitrogen dynamics in the Arctic Ocean

Little is known about the distribution and dynamics of dissolved organic nitrogen (DON) within Arctic Ocean surface waters, though seasonal inputs from both rivers and marine phytoplankton production are likely important. Here we combine multiple datasets to provide the first quasi-synoptic view of DON concentrations in the summertime Arctic Ocean Polar Surface Layer (PSL) and western Arctic shelves, and infer controlling processes. Distributions indicate inputs of DON by Arctic rivers followed by net consumption of up to 70% of this terrigenous material across the resulting salinity gradients over time scales of years. Coupling of DON losses to PSL residence times indicates first order decay constants (λ) of 0.15±0.07yr−1 and 0.08±0.01yr−1 for terrigenous DON in the eastern and western Arctic systems, respectively. Riverine delivery of both inorganic and organic nitrogen have only a minor (<15%) impact on Arctic shelf export production. In the Pacific Ocean-influenced Chukchi Sea, net biological production of ~2μM DON, representing ~8% of net community production, is observed in surface waters following seasonal sea-ice retreat. These findings highlight the contrasting roles and locations of terrigenous versus marine derived DON in the cycling of nitrogen in the surface Arctic Ocean.

Dissolved iron in the Arctic shelf seas and surface waters of the central Arctic Ocean: Impact of Arctic river water and ice‐melt

Concentrations of dissolved (&lt;0.2 μm) Fe (DFe) in the Arctic shelf seas and in the surface waters of the central Arctic Ocean are presented. In the Barents and Kara seas, near‐surface DFe minima indicate depletion of DFe by phytoplankton growth. Below the surface, lower DFe concentrations in the Kara Sea (∼0.4–0.6 nM) than in the Barents Sea (∼0.6–0.8 nM) likely reflect scavenging removal or biological depletion of DFe. Very high DFe concentrations (&gt;10 nM) in the bottom waters of the Laptev Sea shelf may be attributed to either sediment resuspension, sinking of brine or regeneration of DFe in the lower layers. A significant correlation (R2 = 0.60) between salinity and DFe is observed. Using δ18O, salinity, nutrients and total alkalinity data, the main source for the high (&gt;2 nM) DFe concentrations in the Amundsen and Makarov Basins is identified as (Eurasian) river water, transported with the Transpolar Drift (TPD). On the North American side of the TPD, the DFe concentrations are low (&lt;0.8 nM) and variations are determined by the effects of sea‐ice meltwater, biological depletion and remineralization and scavenging in halocline waters from the shelf. This distribution pattern of DFe is also supported by the ratio between unfiltered and dissolved Fe (high (&gt;4) above the shelf and low (&lt;4) off the shelf).

The Arctic Ocean marine carbon cycle: evaluation of air-sea CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; exchanges, ocean acidification impacts and potential feedbacks

Abstract. At present, although seasonal sea-ice cover mitigates atmosphere-ocean gas exchange, the Arctic Ocean takes up carbon dioxide (CO2) on the order of −66 to −199 Tg C year−1 (1012 g C), contributing 5–14% to the global balance of CO2 sinks and sources. Because of this, the Arctic Ocean has an important influence on the global carbon cycle, with the marine carbon cycle and atmosphere-ocean CO2 exchanges sensitive to Arctic Ocean and global climate change feedbacks. In the near-term, further sea-ice loss and increases in phytoplankton growth rates are expected to increase the uptake of CO2 by Arctic Ocean surface waters, although mitigated somewhat by surface warming in the Arctic. Thus, the capacity of the Arctic Ocean to uptake CO2 is expected to alter in response to environmental changes driven largely by climate. These changes are likely to continue to modify the physics, biogeochemistry, and ecology of the Arctic Ocean in ways that are not yet fully understood. In surface waters, sea-ice melt, river runoff, cooling and uptake of CO2 through air-sea gas exchange combine to decrease the calcium carbonate (CaCO3) mineral saturation states (Ω) of seawater while seasonal phytoplankton primary production (PP) mitigates this effect. Biological amplification of ocean acidification effects in subsurface waters, due to the remineralization of organic matter, is likely to reduce the ability of many species to produce CaCO3 shells or tests with profound implications for Arctic marine ecosystems