Simpson Lagoon Research Articles

Seasonality of submarine groundwater discharge to an Arctic coastal lagoon

AbstractSupra‐permafrost submarine groundwater discharge (SGD) in the Arctic is potentially important for coastal biogeochemistry and will likely increase over the coming decades owing to climate change. Despite this, land‐to‐ocean material fluxes via SGD in Arctic environments have seldom been quantified. This study used radium (Ra) isotopes to quantify SGD fluxes to an Arctic coastal lagoon (Simpson Lagoon, Alaska) during five sampling periods between 2021 and 2023. Using a Ra mass balance model, we found that the SGD water flux was substantial and dependent on environmental conditions. No measurable SGD was detected during the spring sampling period (June 2022), when the lagoon was partially ice‐covered. During ice‐free periods, the main driver of SGD in this location is wind‐driven lagoon water level changes, not tides, which control surface water recirculation through sediments along the lagoon boundary. A combination of wind strength and direction led to low SGD fluxes in July 2022, with an SGD flux of (6 ± 3) × 106 m3 d−1, moderate fluxes in August 2021 and July 2023, which had an average flux of (17 ± 9) × 106 m3 d−1, and high fluxes in October 2022, at (79 ± 16) × 106 m3 d−1. This work demonstrates how soil and environmental conditions in the Arctic impact Ra mobilization, laying a foundation for future SGD studies in the Arctic and shedding light on the major processes driving Ra fluxes in this important environment.

Feeding on epibenthic zooplankton by Long‐tailed Ducks: patch structure, profitability, and food web implications

AbstractModels of the trophic needs and impacts of mobile predators in food web networks typically do not consider interactions between prey dispersion and threshold prey densities needed for profitable foraging. As a result, the biomass of predators that can be supported, or direct and indirect impacts of those predators on other food web components, may be poorly estimated. In Simpson Lagoon on the U.S. Arctic coast, epibenthic amphipods and especially mysid shrimp comprised most of the diets of fish, and of Long‐tailed Ducks (Clangula hyemalis) which strongly dominated prey consumption. Based on mean prey densities and gross estimates of prey biomass consumed, earlier studies estimated that continuous immigration of mysids into the lagoon was needed to support the predators. Comparison of variances from net samples vs. different probability density functions (PDFs) around reported means indicated that prey were not normally distributed, and instead occurred in patches with a skewed and wide range of densities. We used the functional response of captive Long‐tailed Ducks eating mysids, and a foraging energetics model, to identify minimum prey densities these diving ducks needed to feed profitably. Based on PDFs that assumed prey densities in all 1‐m2 cells (patches for single feeding dives on potential mysid swarms) were independent, we simulated prey grids with slightly skewed to highly skewed distributions for the reported sample means. Results showed that the greater the range of patch densities, the smaller the fraction of prey biomass that was profitably available to the ducks, thereby increasing the requisite immigration of mysids. Consumption by ectothermic predators further decreased prey available and advanced the date and increased the amount of mysid influx required. The models also showed that the birds had to seek areas with non‐independent clusters of high‐density feeding patches as prey declined in late summer. Thus, spatially continuous measures of patch structure over larger scales are needed to estimate the fraction of prey that is functionally available. Our study emphasizes that when estimating trophic needs and impacts of mobile endothermic predators, simple means of prey density can be misleading, owing to interactions of prey patch structure with profitability thresholds.

Marine mammal visual and acoustic surveys near the Alaskan Colville River Delta

Information about the occurrence of marine mammals near the Colville River Delta (CRD), Beaufort Sea, Alaska is limited for most species expected to occur in this region. As part of marine mammal monitoring and mitigation for a seismic acquisition program August 25–September 30, 2014, we recorded marine mammal occurrence in a ~ 30 km2 survey area between the Spy Islands and Oliktok Point near Simpson Lagoon using a combination of visual and acoustic monitoring methods. Visual effort totaled 632 h, occurring 18–20 h/day during all daylight hours by observers aboard three small survey vessels. In addition, an Inupiat observer and seal hunter from the village of Nuiqsut conducted a small-vessel survey to investigate locations of Phoca largha haul-out sites. A total of 102 individual marine mammals were recorded from five species: P. largha, Pusa hispida, Ursus maritimus, Erignathus barbatus, and Delphinapterus leucas. Over 400 h of acoustic data were recorded using second-generation Ecological Acoustic Recorders deployed on the seafloor at three locations. Calls were identified for D. leucas, Balaena mysticetus, E. barbatus, and P. hispida. Results provide valuable information on marine mammal occurrence for the Beaufort Sea CRD during summer/fall, an area proposed for potential offshore oil and gas development.

A multi-proxy investigation of late-Holocene temperature change and climate-driven fluctuations in sediment sourcing: Simpson Lagoon, Alaska

The significant and ongoing environmental changes in Arctic regions demonstrate the need for quantitative, high-resolution records of pre-industrial climate change in this climatically sensitive region; such records are fundamental for understanding recent anthropogenic changes in the context of natural variability. Sediment contained within Arctic coastal environments proximal to large fluvial systems has the ability to record paleoclimate variability on subdecadal to decadal scale resolution, on par with many other terrestrial climate archives (i.e. lake sediments, ice cores). Here, we utilize one such sediment archive from Simpson Lagoon, Alaska, located adjacent to the Colville River Delta to reconstruct temperature variability and fluctuations in sediment sourcing over the past 1700 years. Quantitative reconstructions of summer air temperature are obtained using the branched glycerol dialkyl glycerol tetraether (brGDGT)-derived methylation index of branched tetraethers (MBT’)/cyclization ratio of branched tetraether (CBT) paleothermometer and reveal temperature departures correlative with noted climate events (i.e. ‘Little Ice Age’, ‘Medieval Climate Anomaly’). In addition, temporal variability in sediment sourcing to the lagoon, determined using a multi-proxy approach (i.e. granulometry, elemental analysis, clay mineralogy), broadly corresponds with temperature fluctuations, indicating relative increases in fluvial sediment discharge during colder intervals and decreased river discharge/increased coastal erosion during warmer periods. The Simpson Lagoon record presented in this study is the first temperature reconstruction, to our knowledge, developed from coastal marine sediments in the Alaskan Beaufort Sea.

Distribution of branched GDGTs in surface sediments from the Colville River, Alaska: Implications for the MBT′/CBT paleothermometer in Arctic marine sediments

AbstractSignificant climate fluctuations in the Arctic over the recent past, and additional predicted future temperature changes, highlight the need for high‐resolution Arctic paleoclimate records. Arctic coastal environments supplied with terrigenous sediment from Arctic rivers have the potential to provide annual to subdecadal resolution records of climate variability over the last few millennia. A potential tool for paleotemperature reconstructions in these marine sediments is the revised methylation index of branched tetraethers (MBT′)/cyclization ratio of branched tetraethers (CBT) proxy based on branched glycerol dialkyl glycerol tetraethers (brGDGTs). In this study, we examine the source of brGDGTs in the Colville River, Alaska, and the adjacent Simpson Lagoon and reconstruct temperatures from Simpson Lagoon sediments to evaluate the applicability of this proxy in Arctic estuarine environments. The Colville catchment soils, fluvial sediments, and estuarine sediments contain statistically similar brGDGT distributions, indicating that the brGDGTs throughout the system are soil derived with little alteration from in situ brGDGT production in the river or coastal waters. Temperatures reconstructed from the MBT′/CBT indices for surface samples show good agreement with regional summer (June through September) temperatures, suggesting a seasonal bias in Arctic temperature reconstructions from the Colville system. In addition, we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 years, revealing an overall warming trend in the twentieth century that is consistent with trends observed in regional instrumental records. These results support the application of this brGDGT‐based paleotemperature proxy for subdecadal‐scale summer temperature reconstructions in Arctic estuaries containing organic material derived from sediment‐laden, episodic rivers.

Sources of organic matter in sediments of the Colville River delta, Alaska: A multi-proxy approach

Thawing of permafrost and subsequent release of organic carbon in the warming Arctic has great potential to influence carbon cycling between the land and ocean. Here, we investigated temporal and spatial differences of organic carbon sources in sediments of Colville River delta and the adjacent Simpson Lagoon, Alaska (USA) over the last ∼50years, using a multi-proxy approach (lignin, fatty acids, sterols, bulk and compound-specific 13C isotopes). Stations closer to the river mouth showed greater inputs of soil and litter-derived terrestrial material based on the terrestrial inputs indicator (Λ8), soil biomarker (3,5-Bd), and degradation index ([Ad/Al]v), as well as stronger and more frequent watershed-flushing events, coupled with Colville River discharge events, than stations in the lagoon. Values of Λ8, 3,5-Bd, and [Ad/Al]v in sediments ranged from 0.75–2.69, 0.02–0.44mg/100mg OC, and 0.23–0.85, respectively. The increase of terrestrial inputs in sediments near the delta for the last ∼50years is most likely due to increase of river discharge under warmer temperatures in recent decades. Coastal erosion and inputs from other river sources (e.g., Kuparuk and Mackenzie Rivers) also contribute to the organic carbon in sediments of the delta. Rudimentary fatty acid indices reflected two distinct groups of bacteria in these sediments. Additionally, the sterol biomarker 24-ethylcholest-5-en-3β-ol is useful to track peat inputs in the Arctic.

Late Holocene sedimentation in a high Arctic coastal setting: Simpson Lagoon and Colville Delta, Alaska

Arctic coastal environments near major river outfalls, like Simpson Lagoon, Alaska and the adjacent Colville River Delta, potentially contain high-resolution sediment records useful in elucidating late Holocene Arctic sediment transport pathways and coupled terrestrial-ocean evidence of paleoclimate variability. This study utilizes a multi-tracer geochronology approach (137Cs, 239,240Pu, and 14C) tailored for high-latitude environments to determine the age models for cores collected from Simpson Lagoon, and to date seismic boundaries in shallow acoustic reflection data (CHIRP) to examine late Holocene infill patterns. Modern (~100y) sediment accumulation rates range from <0.02 to 0.46±0.04cmy−1, with a primary depocenter in western Simpson Lagoon adjacent to the Colville Delta and a secondary depocenter in eastern Simpson Lagoon. CHIRP reflectors, age-constrained by 14C analysis, reveal rapid late Holocene (0–3500y BP) transgression consistent with high modern shoreline retreat rates. The western depocenter contains >5m of late Holocene interbedded sediments, likely derived primarily from the Colville River, with onset of accumulation occurring prior to ~3500y BP. A paleo-high in central Simpson Lagoon, separating the two depocenters, was subaerially exposed prior to ~600y BP. The millimeters-per-year sedimentation rates across the lagoon, coupled with the undisturbed, interbedded sediment record, indicate that these settings hold great potential to develop new Arctic paleoenvironmental records.

Sources of terrigenous inputs to surface sediments of the Colville River Delta and Simpson's Lagoon, Beaufort Sea, Alaska

AbstractThe provenance of sediments and particulate organic carbon (POC) in the Colville River delta and adjacent Simpson's Lagoon, in the Alaskan Beaufort Sea, was investigated using a variety of bulk and molecular techniques, including stable and radiocarbon isotopes, neodymium isotopes, algal pigments, and lignin‐phenols. Additionally, stable carbon isotopes and lignin‐phenols were analyzed on four different density fractions from sediments. The Colville River, the largest river in North America with a watershed exclusively located in the high‐Arctic tundra, was an important source of terrestrial POC to the western edge of the Lagoon, shown by extremely old radiocarbon ages (fraction modern of 0.165 ± 0.001 close to the river mouth up to 0.418 ± 0.002 farther away). Stations without northern protective barrier islands had large amounts of marine POC input, and evidence of benthic microalgae was found in one area of the Lagoon (chlorophyll‐a concentration 35.0 µg gOC−1 in the high‐algal biomass area compared to 1 to 7 µg gOC−1 outside of it). Stations in the middle and eastern end of the Lagoon showed significant sediment input from coastal erosion (input of peat‐indicating non‐lignin‐phenols 0.079 mg (100mgOC)−1 in the eastern lagoon compared to 0.022 mg (100mgOC)−1 near the Colville delta), and on the eastern end of the Lagoon there was evidence of input of Mackenzie River POC, shown with neodymium isotopes and also COP. POC inputs derived from rivers, coastal erosion, and marine productivity were quantified using a ternary mixing model and showed that fluvial supply and coastal erosion were the dominant carbon sources to the Lagoon. This constitutes the first study of POC delivery by the Colville River into a nearshore region and illustrates that continued warming of the high Arctic tundra will likely lead to increased riverine POC delivery to this region of the world.

Do common eiders nest in kin groups? Microgeographic genetic structure in a philopatric sea duck

We investigated local genetic associations among female Pacific common eiders (Somateria mollissima v-nigrum) nesting in a stochastic Arctic environment within two groups of barrier islands (Simpson Lagoon and Mikkelsen Bay) in the Beaufort Sea, Alaska. Nonrandom genetic associations were observed among nesting females using regional spatial autocorrelation analyses for distance classes up to 1000 m in Simpson Lagoon. Nearest-neighbour analyses identified clusters of genetically related females with positive lr values observed for 0-13% and 0-7% of the comparisons in Simpson Lagoon and Mikkelsen Bay, respectively, across years. These results indicate that a proportion of females are nesting in close proximity to more genetically related individuals, albeit at low frequency. Such kin groupings may form through active association between relatives or through natal philopatry and breeding site fidelity. Eiders nest in close association with driftwood, which is redistributed annually by seasonal storms. Yet, genetic associations were still observed. Microgeographic structure may thus be more attributable to kin association than natal philopatry and site fidelity. However, habitat availability may also influence the level of structure observed. Regional structure was present only within Simpson Lagoon and this island group includes at least three islands with sufficient driftwood for colonies, whereas only one island at Mikkelsen Bay has these features. A long-term demographic study is needed to understand more fully the mechanisms that lead to fine-scale genetic structure observed in common eiders breeding in the Beaufort Sea.

Hierarchical Spatial Genetic Structure of Common Eiders (Somateria mollissima) Breeding along a Migratory Corridor

Documentation of spatial genetic discordance among breeding populations of Arctic-nesting avian species is important, because anthropogenic change is altering environmental linkages at micro- and macrogeographic scales. We estimated levels of population subdivision within Pacific Common Eiders (Somateria mollissima v-nigrum) breeding on 12 barrier islands in the western Beaufort Sea, Alaska, using molecular markers and capture—mark—recapture (CMR) data. Common Eider populations were genetically structured on a microgeographic scale. Regional comparisons between populations breeding on island groups separated by 90 km (Mikkelsen Bay and Simpson Lagoon) revealed structuring at 14 microsatellite loci (FST = 0.004, P < 0.01), a nuclear intron (FST = 0.022, P = 0.02), and mitochondrial DNA (ΦST = 0.082, P < 0.05). The CMR data (n = 34) did not indicate female dispersal between island groups. Concordance between genetic and CMR data indicates that females breeding in the western Beaufort Sea are strongly philopatric to island groups rather than to a particular island. Despite the apparent high site fidelity of females, coalescence-based models of gene flow suggest that asymmetrical western dispersal occurs between island groups and is likely mediated by Mikkelsen Bay females stopping early on spring migration at Simpson Lagoon to breed. Alternatively, late-arriving females may be predisposed to nest in Simpson Lagoon because of the greater availability and wider distribution of nesting habitat. Our results indicate that genetic discontinuities, mediated by female philopatry, can exist at microgeographic scales along established migratory corridors.

Distributional patterns of fishes in an Alaskan Arctic Lagoon

In summer, the fish community of Simpson Lagoon and adjacent coastal waters of the Beaufort Sea was dominated by two marine species (Arctic cod, fourhorn sculpin) and three anadromous species (Arctic and least cisco, Arctic char). The anadromous species remained in the relatively warm and brackish waters near shore and demonstrated an affinity for shoreline edges, particularly the mainland shoreline where species occurrence and catch per unit effort (CPUE) were highest. Spatial segregation was low, presumably reflecting the migratory nature of these species. Marine species were less restricted to nearshore waters in summer and were typically the only species present in winter because anadromous species return to rivers, lakes and deltas to spawn or overwinter. Winter CPUE was low and consisted primarily of Arctic cod and fourhorn sculpin.

Ecological Studies of Arctic Cod (Boreogadus saida) in Beaufort Sea Coastal Waters, Alaska

Fish use of Beaufort Sea coastal waters was examined during summer and winter periods 1977–80. Arctic cod (Boreogadus saida) were abundant but their occurrence was highly variable. They accounted for 8–78% of all fish caught in Simpson Lagoon during two summers, and 0.4–100% of catches at various coastal sites in winter. Arctic cod increased in abundance in the lagoon during late summer and some association was noted between their numbers and higher salinities but not temperature or turbidity. Some cod remained in shallow waters in early winter but deeper areas were used through the winter, and the highest catch rate was recorded 175 km offshore. Principal foods of the cod in nearshore waters were mysids (Mysis litoralis, M. relicta), amphipods (Onisimus glacialis), and copepods. The cod caught were generally small (60–170 mm) and young (ages 1–3). Most males matured at ages 2–3 and females at age 3. These size, age, and maturity characteristics indicate a life history strategy (r-selection) unlike that typified by many other arctic fish populations, particularly the freshwater and anadromous species which tend to be slow growing, late maturing and long-lived (K-selection).Key words: Arctic cod, Boreogadus saida; Beaufort Sea, distribution, life history strategy

Wind and current patterns in an arctic coast Lagoon

The response of wind-drift currents to the prevailing summer wind regime is reported for Simpson Lagoon on the Beaufort Sea (Arctic Ocean) coast of Alaska. Wind and current measurements were taken over the period July 17 to October 20 and August 11 to September 18, 1972, respectively, at a site eastward of the Colville River delta. Mean wind speeds and the frequency of occurrence of westerly storms tend to increase from July to October. Prevailing currents within the lagoon are towards the W to NW driven by the prevailing northeasterly winds. Relatively rapid reversals of current direction occur in response to alternating easterly and westerly winds. Cross correlations of power spectra of the filtered E-W components of the lagoon current record with the concurrent wind data gave a periodicity of 4–5 days at a 70% level of coherence. A linear correlation of −0·83 was obtained between the E-W components of the filtered current record and the wind record, and net water transport (from a progressive current vector analysis) over this period was determined to be towards the WNW with a mean vector velocity of 10·6 cm/sec.