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Reduced sea ice has made the Arctic Ocean more accessible for vessel traffic. In turn, the heightened interest to better understand rapidly changing sea ice dynamics, ecosystems, and related ocean processes in the Arctic Ocean has led to closer interactions with and the need to avoid potential conflicts between scientific researchers and Indigenous coastal communities. In particular, researchers need to minimize spatial and temporal overlap of science activities with subsistence hunts as the Arctic is essential to Indigenous communities for their food security and cultural heritage. In this regard, a Community and Environmental Compliance Standard Operating Procedure (CECSOP) was recently developed for the R/V Sikuliaq, which is owned by the National Science Foundation and operated by the University of Alaska Fairbanks College of Fisheries and Ocean Sciences and is part of the University-National Oceanographic Laboratory System. The CECSOP was developed with input and guidance from Alaska Indigenous community groups, state and federal agencies, and sea-going scientists. Here the document's basic principles and procedures are described, as well as its utility in helping guide constructive discussions and interactions between scientific users of R/V Sikuliaq and subsistence hunting communities when research and subsistence hunt activities have spatial and temporal overlap. The CECSOP is a “living” document and subject to future modifications and improvements. It may serve as a model for other scientific, commercial and industrial vessel operators to ensure best practices between subsistence hunting communities and vessel operators in the Arctic.

The Northeast USA is experiencing severe impacts of a changing climate, including increased winter temperatures and accelerated relative sea level rise (RSLR). The sediment-poor, organic-rich nature of many Southern New England salt marshes makes them particularly vulnerable to these changes. In order to assess how marsh accretion has changed over time, we returned to Narragansett Bay, RI where salt marsh vertical accretion rates were documented almost 30 years ago. Using radionuclide tracers (210Pb and 137Cs), we observe no significant change in overall accretion rates (0.27–0.69 cm year−1) compared to historical averages (0.24–0.60 cm year−1), but we document a shift in how these marshes maintain elevation. Organic matter now plays a smaller role in contributing to vertical accretion across all study sites, declining by 22 % on average. We attribute this reduction to potentially higher decomposition rates fueled by higher water temperature. Inorganic matter also contributes less to accretion (declining by 44 % on average at marshes located more internal to the estuary), likely due to diminishing sediment supply in this region. With organic and inorganic solids accounting for less of the total accretion, several of the marshes are experiencing symptoms of swelling, with water and porespace contributing more towards accretion compared to historical values. Accretion rates (0.27–0.45 cm year−1) at these organic-rich (>40 % sediment organic matter) marshes are predominantly lower than the current (30 years) rate of RSLR (0.41 ± 0.07 cm year−1). These results, combined with the increased rate of RSLR and the hardened shorelines inhibiting landward migration, call into question the long-term survivability of these marshes.

et al., Measurements of 129I carried out on sea ice samples collected in the central Arctic Ocean in 2007 revealed relatively high levels in the range of 100-1400×107 at L-1 that are comparable to levels measured in the surface mixed layer of the ocean at the same time. The 129I/127I ratio in sea ice is much greater than that in the underlying water, indicating that the 129I inventory in sea ice cannot be supported by direct uptake from seawater or by iodine volatilization from proximal (nearby) oceanic regimes. Instead, it is proposed that most of the 129I inventory in the sea ice is derived from direct atmospheric transport from European nuclear fuel reprocessing plants at Sellafield and Cap La Hague. This hypothesis is supported by back trajectory simulations indicating that volume elements of air originating in the Sellafield/La Hague regions would have been present at arctic sampling stations coincident with sampling collection., This work was partially funded by the Ministerio de Educación y Ciencia (MEC) of Spain (POL2006–00449), the prize ICREA Academia, funded by the Generalitat de Catalunya (PM), and the fellowship AP2006–03071 (PC-M). PM was supported in part by a Gledden Visiting Fellowship awarded by the Institute of Advanced Studies at The University of Western Australia.

Two independent methods were used to estimate particle export fluxes of metals in the Gulf of Maine and Scotian Shelf. The first method used measurements of particulate trace metals (Cd, Cu, Fe and Pb) and metal/ 234 Th ratios on large (>53 µm), rapidly sinking, particles together with prior estimates of 234 Th/ 238 U disequilibrium to quantify the particle export flux of these metals. The second method adopted a mass balance approach whereby measurements of the distribution of dissolved ( 234 Th/ 238 U method, indicating that metal transport through shelf/slope regimes can be reasonably characterized using relatively limited data sets. Specifically, these results indicate that ~40–60% of the Pb and Zn inputs to the Gulf of Maine and Scotian Shelf are scavenged and exported to the sediments, whereas only ~5–15% of the Ni and Cu inputs are removed by particle export, as would be anticipated based on their respective particle affinities.

Measurements of groundwater-dissolved inorganic nitrogen (nitrate + nitrite + ammonia) and phosphate concentrations were combined with recent, radium-based, submarine groundwater discharge (SGD) fluxes and prior estimates of SGD determined from Darcy’s Law, a hydrologic model, and total recharge to yield corresponding SGD nutrient fluxes to Ninigret, Point Judith, Quonochontaug, and Winnapaug ponds, located in southern Rhode Island. Results range from 80 to279 mmol N m−2 year−1 and 4 to 15 mmol P m−2 year−1 for Ninigret, 48 to 265 mmol N m−2 year−1 and 4 to 23 mmol P m−2 year−1 for Point Judith, 31 to 62 mmol N m−2 year−1 and 1 to 2 mmol P m−2 y−1 for Quonochontaug, and 668 to 1,586 mmol N m−2 year−1 and 29 to 70 mmol P m−2 year−1 for Winnapaug ponds, respectively. On a daily basis, the SGD supply of dissolved inorganic nitrogen and phosphorus is estimated to represent ∼1–6 % of the total amount of these nutrients in surface waters of Ninigret, Point Judith, and Quonochontaug ponds and up to 84 and 17 % for Winnapaug, respectively, which may reflect a greater SGD nutrient supply to this pond because of the proximity of fertilized golf courses. With regard to the total external input of these essential nutrients, SGD represents 29–45 % of dissolved inorganic nitrogen input to Ninigret, Point Judith, and Quonochontaug ponds and as much as 93 % for Winnapaug pond. For phosphorus, the contribution from SGD represents 59–85 % of the total external input for Ninigret, Point Judith, and Quonochontaug ponds and essentially all of the phosphorus input to Winnapaug pond. Estimated rates of primary productivity potentially supported by the average supply of dissolved inorganic nitrogen from SGD range from 10 g C m−2 year−1 for Ninigret, 13 g C m−2 year−1 for Point Judith, 4 g C m−2 year−1 for Quonochontaug, and as high as 84 g C m−2 y−1 for Winnapaug pond. The imputed SGD-derived rates of primary productivity represent 4–9 % of water column primary production for Ninigret, Point Judith, and Quonochontaug ponds, and 74 % for Winnapaug pond, a result that is reasonably comparable to several other coastal environments where estimates of SGD nutrient supply have been reported. The implication is that SGD represents an ecologically significant source of dissolved nutrients to the coastal salt ponds of southern Rhode Island and, by inference, other coastal systems.

In 1999, the large surface-rupturing earthquakes of Izmit and Duzce completed a 60-year cycle that included a westward migration of nine consecutive large earthquake failures (>50 km surface rupture), which started with the 1939 Erzincan earthquake in eastern Turkey. In this study, we focused on seismic cycles and seismic risk predictability along the North Anatolian Fault (NAF). Toward the west end of the NAF (26°E–32°E, i.e. Bolu), large earthquake frequency is measured from either historic earthquake catalogs, or geologic records from isolated outcrops and marine sediment cores from the Marmara Sea. In comparison, the eastern part of the NAF zone (32°E–42°E) is less well documented by palaeo-seismologic archives. Thus, the sediment records of lake basins located on the eastern NAF zone constitute a unique opportunity for testing a new palaeo-seismologic approach. To this end, we used a diverse array of complementary methods involving: (1) a 600-km transect of fault-related lakes, (2) sedimentologic observations on cores from six lakes, and (3) a comparison between records of catastrophic sediment transfers in lakes (i.e. radionuclide chronomarkers and erosion tracers) and historic earthquake reports. Our study indicates that lakes along the NAF are sensitive geologic recorders of large surface-rupturing earthquakes (surface-wave magnitude (M s) ≥ 6.9); smaller intensities are not recorded. The most responsive lake systems exhibit increases in sediment accumulation by a factor of >40 for a >3-m strike-slip displacement (M s ≥ 7). However, based on results from the 1939 Erzincan earthquake (M s = 7.8) chronostratigraphic marker, large surface-rupturing earthquakes are detected only by certain lake records and not by others. Matching multiple lake records along the NAF provides information both on the location of a surface rupture of a paleo-earthquake as well as its magnitude. Finally, the shallow lake basins along the NAF could potentially document cycles of large seismic events for at least the late Holocene.

Measurements of particle size-fractionated POC/ 234 Th ratios and 234 Th and POC fluxes were conducted using surface-tethered, free-floating, sediment traps and large-volume in-situ pumps during four cruises in 2004 and 2005 to the oligotrophic eastern Mediterranean Sea and the seasonally productive western Mediterranean and northwest Atlantic. Analysis of POC/ 234 Th ratios in sediment trap material and 10, 20, 53, 70, and 100 μm size-fractionated particles indicate, for most stations, decreasing ratios with depth, a weak dependence on particle size, and ratios that converge to ∼1–5 μmol dpm −1 below the euphotic zone (∼100–150 m) throughout the contrasting biogeochemical regimes. In the oligotrophic waters of the Aegean Sea, 234 Th and POC fluxes estimated using sediment traps were consistently higher than respective fluxes estimated from water-column 234 Th– 238 U disequilibrium, observations that are attributed to terrigenous particle scavenging of 234 Th. In the more productive western Mediterranean and northwest Atlantic, 234 Th and POC fluxes measured by sediment trap and 234 Th– 238 U disequilibrium agreed within a factor of 2–4 throughout the water column. An implication of these results is that estimates of POC export by sediment traps and 234 Th– 238 U disequilibrium can be biased differently because of differential settling speeds of POC and 234 Th-carrying particles.

Seasonal changes in Th scavenging and particle aggregation were determined along two shelf-basin transects in the western Arctic Ocean during the spring (May–June) and summer (July–August) of 2002 and 2004. Measurements of dissolved and particulate 234 Th and 228 Th activities were used to quantify Th residence times and reversible rates of Th sorption and particle aggregation. Prior to the spring bloom in 2002, 234 Th and 228 Th residence times were equal and Th scavenging was concordant, indicating predominately steady-state conditions. In contrast, scavenging of 234 Th and 228 Th in the summer of 2002 and the spring and summer of 2004 was discordant, indicating a departure in scavenging rates from steady-state conditions during periods of seasonally high biological activity and particle export. Rates of particle aggregation and disaggregation were calculated using a one-dimensional reversible exchange model and 234 Th and 228 Th activities in small (1–53 μm) and large (>53 μm) particles. Maximum rates were determined coincident with the chlorophyll maximum (25–100 m) and increased by an order of magnitude between periods of low and high productivity. These Th measurements provide evidence that seasonally enhanced rates of particle aggregation might increase the magnitude of the particulate organic carbon (POC) flux in this Arctic regime.

Measurements of 234 Th/ 238 U disequilibria and particle size-fractionated (1, 10, 20, 53, 70, 100mm) organic C and 234 Th were made to constrain estimates of the export flux of particulate organic C (POC) from the surface waters of the Ligurian, Tyrrhenian and Aegean Seas in March–June 2004. POC exported from the surface waters (75–100 m depth) averaged 9.2 mmol m � 2 d � 1 in the Ligurian and Tyrrhenian Seas (2.370.5–14.973.0 mmol m � 2 d � 1 ) and 0.9 mmol m � 2 d � 1 in the Aegean Sea. These results are comparable to previous measurements of 234 Th-derived and sediment-trap POC fluxes from the upper 200 m in the Mediterranean Sea. Depth variations in the POC/ 234 Th ratio suggest two possible controls. First, decreasing POC/ 234 Th ratios with depth were attributed to preferential remineralization of organic C. Second, the occurrence of maxima or minima in the POC/ 234 Th ratio near the DCM suggests influence by phytoplankton dynamics. To assess the accuracy of these data, the empirical 234 Th-method was evaluated by quantifying the extent to which the 234 Thbased estimate of POC flux, PPOC, deviates from the true flux, FPOC, defined as the p-ratio (p-ratio ¼ PPOC/FPOC ¼ STh/ SPOC, where S ¼ particle sinking rate). Estimates of the p-ratio made using Stokes’ Law and the particle size distributions of organic C and 234 Th yield values ranging from 0.93–1.45. The proximity of the p-ratio to unity implies that differences in the sinking rates of POC- and 234 Th-carrying particles did not bias 234 Th-normalized POC fluxes by more than a factor of two.

An analysis of the 234 Th method for determining the export flux of particulate organic carbon ( P POC ) from the upper ocean using in situ pumps or water bottles shows that the accuracy of the method (the ratio of the experimental value of P POC divided by the true POC flux, F POC ), defined as the p -ratio, is equal to the mean settling velocity of particulate 234 Th divided by that of POC. Therefore, P POC is equivalent to the true POC flux ( F POC ) and the p -ratio is equal to unity if, and only if, POC and particulate 234 Th have the same mean sinking velocities. A simple particle settling model is discussed that invokes Stokes’ Law settling velocities, volume:surface area ( V :SA) fractionation of C: 234 Th and two assemblages of particles having different sizes and densities. The model is used to illustrate the ranges of parameter values that conform to values of the p -ratio sufficiently close to unity that the experimentally determined POC flux can be considered to be an accurate representation of the true POC flux. Despite the over-simplification of real systems implicit in the model, the results suggest that p -ratios 234 Th on particles is governed by the volume to surface area ( V :SA) ratio of the particles. This results in a greater proportion of 234 Th compared to C being associated with the smaller, more slowly settling particles and, as a result, normalization of the POC flux to the 234 Th flux provides an under-estimate of the former quantity. However, when the smaller particle assemblage dominates the vertical flux, as could occur in open ocean regimes having high aeolian inputs of dense, rapidly settling, inorganic particles, then the p -ratio could exceed unity ( p -ratio >1) resulting in an over-estimate of the POC flux using the 234 Th method. High levels of flocculation associated with phytoplankton blooms in productive regions of the ocean are likely to produce p -ratios approaching unity, because flocs would tend to preserve the V :SA partitioning of the original particle size distribution and thereby minimize differences in the mean settling speeds of POC and particulate 234 Th (Waite, A.W., Hill, P.S., 2006. Flocculation, phytoplankton and the accuracy of 234 Th-based estimates of the vertical flux of particulate organic carbon in the sea. Marine Chemistry in press). Selective sampling of the large particle fraction using, for example, 53-μm screens can produce a more accurate estimate of the true POC flux, but may not entirely shift the p -ratio to a value of unity.

The magnitude of the flux of biogenic particulate organic carbon (POC) exported from the surface waters of the world ocean and remineralized at depth is critical to constraining models of the global carbon cycle, yet remains controversial. The use of upper ocean sediment traps is still one of the primary tools for determining this export flux, although trap fluxes have been shown to vary significantly because of hydrodynamic and sample collection biases. Over the past decade, 234 Th increasingly has been used as a tracer to estimate POC export from the euphotic zone by multiplying the depth-integrated 234 Th flux by the POC/ 234 Th ratio of sinking particles. The accuracy of this technique is highly dependent on the natural variability in the POC/ 234 Th ratio and 234 Th flux, yet the significance of this variability to estimates of POC export remains uncertain. Based on an analysis of new 234 Th and POC data from the Labrador Sea and a review of 25 previous independent field studies, we report that POC export fluxes can vary 2-10 times or more solely because of variability in the POC/ 234 Th ratio and procedures used to estimate the 234 Th flux. Recommended improvements include studies of the biological, chemical, and physical mechanisms controlling 234 Th-organic matter interactions in seawater; detailed comparisons of POC/ 234 Th ratios in size-fractionated and sediment trap material; increased spatial and temporal sampling density of 234 Th; and more standardized procedures to calculate the 234 Th export flux.

Measurements of the naturally occurring radionuclides, 210Po, 210Pb, 228Ra and 226Ra were conducted on water and sediment samples collected during the Arctic Ocean Section (1994) and Beaufort Sea (1995) expeditions and are used to assess circulation and shelf/slope scavenging in the Western Arctic Ocean. 228Ra concentrations are higher over the continental shelves of the Chukchi and Beaufort Seas compared to interior waters, consistent with a shelf source for 228Ra. However, 228Ra/226Ra ratios for Pacific-origin water have a lower end member value (ca. 1.0) compared to literature values of 3.6 for end member 228Ra/226Ra ratios for Atlantic-origin water passing across the shelf of the Laptev Sea. The shift during the 1990s in the position of the axis of the Trans-Polar Drift and the consequent change in the pathways for the flow of freshwater from the Russian continental shelves is reflected in a shift of elevated 228Ra concentrations in surface water from the Lomonosov Ridge to the Mendeleyev Ridge. 210Pb water column distributions in the Eurasian Basin are similar to those measured in the North Atlantic and indicate scavenging residence times of 15–20 yr. 210Pb concentrations are lower in intermediate waters of the Makarov and Canada Basins, because of enhanced scavenging at the continental margin. The lowest 210Pb concentrations (

Radionuclide measurements have been conducted on sediment, seawater and biota samples collected in Chernaya Bay, on the southern coast of Novaya Zemlya, the site of two underwater nuclear tests conducted in the 1950s. 239,240Pu levels in sediments from the central region of Chernaya Bay exceed concentrations of 15,000 Bq/kg, and are among the highest ever reported for the marine environment. It is estimated that approximately 11 TBq of 239,240Pu from the tests has been retained in the sediments of Chernaya Bay. Plutonium from Chernaya Bay is distinguished by 240Pu/239Pu atom ratios of 0.03 that are much lower than ratios of 0.18 typical of global fallout. High levels of 137Cs (Bq/kg) and 60Co (Bq/kg) were also measured in surface sediments in the central regions of Chernaya Bay near the presumed epicentre of the explosions. Applications of a biodi!usion model to excess 210Pb sediment depth pro"les indicate that the distribution of 239,240Pu is governed mainly by sediment mixing in this low sedimentation rate ((0.1 cm/yr) regime and, as a result, most of the 239,240Pu has been retained in the upper 20 cm of the sediment column. Elevated levels of 239,240Pu measured in Macoma (104 Bq/kg), Fucus (15 Bq/kg) and polychaete (1292 Bq/kg) from Chernaya Bay, indicate that 239,240Pu levels in the benthos are comparatively high and that signi"cant uptake has occurred in the food chain. Although levels of 239,240Pu in bottom water from Chernaya Bay are high (4.2 Bq/m3), restricted exchange over the fjord sill limits the present rates of 239,240Pu transport from

The transpolar drift is strongly enriched in 228Ra accumulated on the wide Arctic shelves with subsequent rapid offshore transport. We present new data of Polarstern expeditions to the central Arctic and to the Kara and Laptev seas. Because 226Ra activities in Pacific waters are 30% higher than in Atlantic waters, we correct 226Ra for the Pacific admixture when normalizing 228Ra with 226Ra. The use of 228Ra decay as age marker critically depends on the constancy in space and time of the source activity, a condition that has not yet adequately been tested. While 228Ra decays during transit over the central basin, ingrowth of 228Th could provide an alternative age marker. The high 228Th/228Ra activity ratio (AR = 0.8–1.0) in the central basins is incompatible with a mixing model based on horizontal eddy diffusion. An advective model predicts that 228Th grows to an equilibrium AR, the value of which depends on the scavenging regime. The low AR over the Lomonosov Ridge (AR = 0.5) can be due to either rapid transport (minimum age without scavenging 1.1 year) or enhanced scavenging. Suspended particulate matter load (derived from beam transmission and particulate 234Th) and total 234Th depletion data show that scavenging, although extremely low in the central Arctic, is enhanced over the Lomonosov Ridge, making an age of 3 years more likely. The combined data of 228Ra decay and 228Th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern Eurasian Basin with a river water residence time of at least 3 years.

[1] Particulate organic carbon (POC) export fluxes were estimated in the shelf-slope region of the Chukchi Sea using measurements of 234Th−238U disequilibria and the POC/234Th ratio in large (>53-μm) particles. These export fluxes were used in conjunction with rates of primary productivity and benthic carbon respiration to construct a POC budget for this shelf-slope region. Samples were collected along a series of shelf-basin transects in the spring (May–June) and summer (July–August) of 2004. These stations were previously occupied during the ice covered (spring) and open water (summer) seasons of 2002, allowing for an interannual comparison of export flux. In contrast to 2002, when open water POC fluxes were significantly higher than in the ice-covered period, POC export fluxes in 2004 were similar during the spring (average = 19.7 ± 24.8 mmol C m−2 d−1) and summer (average = 20.0 ± 14.5 mmol C m−2 d−1). The high POC fluxes measured during the spring are attributed to a plankton bloom, as evidenced by exceptionally high rates of primary productivity (average = 124.4 ± 88.1 mmol C m−2 d−1). The shelf-slope budget of particulate organic carbon indicates that 10–20% of primary productivity was exported below 50 m but was not consumed during benthic carbon respiration or burial and oxidation in underlying sediments. Furthermore, a water column−sediment budget of 234Th indicates that particulate material is retained in shelf sediments on a seasonal basis.

Iodine 129 discharged from nuclear fuel reprocessing plants in France and the United Kingdom is transported into the Nordic Seas on timescales of 3 - 5 years. Tracer I-129 is subsequently injected into intermediate waters that overflow the sills between Greenland, Iceland, and Scotland and ventilate the North Atlantic Deep Waters ( NADW). During the early 1990s, discharges of I-129 increased by 600%, resulting in a large, well- resolved tracer " front'' whose passage through the Nordic Seas is presently being observed by a time series of I-129 measurements on the WOCE ( AR7W) section in the Labrador Sea. The highest I-129 levels were measured below depths of 3000 m in Denmark Strait Overflow Water ( DSOW). These levels increased by about 300% between 1997 and 2001 to values > 40 x 10(7) atoms/ L, indicating that the leading edge of the tracer " front'' from the early 1990s was being observed entering the NADW. Using a simple mixing/ advection model, I-129 and CFC 11 results were used to calculate transit times of 0.4 - 2.6 years for the flow of DSOW from formation regions in the Nordic Seas to the Labrador Sea. Measurements on samples collected in the Irminger Sea in 2001 gave transit times of 0.3 years for core DSOW immediately south of Denmark Strait and about 2 years for locations off the southern tip of Greenland. An increase in DSOW transit times observed in the Labrador Sea between 1999 and 2001 probably reflects a more general weakening in the subpolar gyre of the North Atlantic during the 1990s.

Dissolved and acetic acid leachable particulate Al ([Al]HAc) concentrations have been measured as a time series during a spring phytoplankton bloom in Bedford Basin off Nova Scotia, Canada. Two factors were observed to influence Al levels: the spring bloom and river runoff. Changes in dissolved Al and [Al]HAc associated with intense biological activity resulted in a 55–65 n m (40%) decrease in dissolved Al and a coincident similar increase in [Al]HAc over 15–20 days. The intensity of Al removal is apparently a function of biogenic particle loads. A pulse in river runoff caused dissolved Al to increase roughly 10 fold (up to 1130 n m ) and [Al]HAc by nearly 4 fold (up to 175 n m ) in the surface 5 m. These data indicate that biological activity can significantly alter concentrations of Al in coastal waters and distributions among dissolved and particulate forms. In the presence of strong sources, such as river runoff, these effects can be obscured.