Mikkelsen Bay Research Articles

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.

Mudstone Sedimentation at High Latitudes: Ice as a Transport Medium for Mud and Supplier of Nutrients

Abstract Controls on mudstone deposition at high latitudes are poorly known relative to low latitudes. In recent sediments deposited in these environments, ice significantly influences sediment transport and primary productivity. The products of ice transport are relatively well known in glacimarine settings, but are less well known from below melting sea ice. This latter setting is significant as today it is associated with high primary organic productivity. The aim of this study is to assess how sea ice might have controlled lithofacies variability and organic-matter distribution and preservation in an ancient marine, siliciclastic mudstone-dominated succession deposited at high latitudes. Combined sedimentary logging, optical and electron optical (backscattered electron imagery), geochemical, and isotopic methods were used to determine sample variability in forty-five samples collected from the Lower Cretaceous succession in the Mikkelsen Bay State #1 borehole (North Slope, Alaska). The succession overall fines upward and contains muddy sandstones and sand- and silt-bearing, clay-rich mudstones towards its base in contrast to clay-rich and clay-dominated mudstones towards its top. Some of the mudstone units exhibit thin (< 5 mm), relic-beds that fine upward weakly. In some units small (0.5 mm), bed-parallel silt-filled microburrows disrupt depositional laminae whereas in others pervasive burrowing completely obliterates original depositional textures. Many of the units are pelleted. These mudstones are unusual in that they contain minor but very striking outsize grains, composed of subrounded to rounded sand and granule-size material. In addition, they are good petroleum source rocks, with between 2.8 and 5.9 wt % total organic carbon, of predominantly Type II kerogen. The organic matter has an isotopic signature ranging from −25.4‰ δ13C to −28.1‰ δ13C. Thin tuffs (< 20 mm) and carbonate-cemented units are also present. Given the absence of significant polar ice in the Early Cretaceous the outsized grains are interpreted to have been deposited from a combination of melting, dirty anchor, and fast ice. The mud fraction, which forms the bulk of the sediment, is interpreted to have been deposited from melting, sediment-laden frazil ice, and fast ice. After deposition sediments were partially reworked by bottom currents generated by brine rejection during sea ice formation. Sympagic organisms, grazing on algae and bacteria both within and below the ice, pelleted the sediment. Bioturbation, which varies through the succession, indicates that sedimentation probably occurred beneath a predominantly oxic or dys-oxic water column. In this setting productivity was fueled by nutrients released from melting sea ice in the marginal ice zone. The good petroleum source potential of these mudstones is attributed to high organic productivity coupled to episodic and rapid sedimentation rather than existence of bottom-water anoxia linked to upwelling. Because sea-ice rafting was probably the dominant sediment transport mechanism it is not appropriate to use sequence stratigraphic methodology to predict lithofacies variability in this environment.

ABSTRACT: A High Resolution Study of Petroleum Source Rock Variation, Lower Cretaceous (Hauterivian and Barremian) of Mikkelsen Bay, North Slope, Alaska

ABSTRACT: A High Resolution Study of Petroleum Source Rock Variation, Lower Cretaceous (Hauterivian and Barremian) of Mikkelsen Bay, North Slope, Alaska

Stock Origins of Dolly Varden Collected from Beaufort Sea Coastal Sites of Arctic Alaska and Canada

Abstract Anadromous northern Dolly Varden Salvelinus malma support a summer subsistence fishery in Beaufort Sea coastal waters. These same waters coincide with areas of oil and gas exploration and development. The purpose of this study was to assess variation in stock origins of Dolly Varden collected from sites along 400 km of Beaufort Sea coast. Mixed-stock analyses (MSA) of allozyme data were used to compare collections from four sites (Endicott near Prudhoe Bay, Mikkelsen Bay, and Kaktovik in Alaska and Phillips Bay in Canada) and to assess variation in stock contributions among summer months and between 1987 and 1988. The MSA estimates for individual stocks were summed into estimates for three stock groups: western stocks from the area near Sagavarnirktok River and Prudhoe Bay (SAG), Arctic National Wildlife Refuge stocks (Arctic Refuge), and Canadian stocks. The MSA of Endicott samples taken in 1987 and 1988 did not differ among months in terms of contributions from local SAG stocks (range, 71–95%)....

Permafrost thicknesses in the Oliktok Point, Prudhoe Bay and Mikkelsen Bay areas of Alaska

An improved map of the thickness of ice-bearing permafrost in northern Alaska has been constructed by combining the previous data of Osterkamp and Payne (1981) with new data obtained by analyses and interpretation of recently released well logs. The new map provides greater detail and increased coverage, especially in offshore areas. Ice-bearing permafrost reached a maximum thickness of ≈ 629 m in three areas. This suggests that the permafrost thickness (depth to 0°C) may be on the order of 670–680 m. Permafrost thickness may be < 200 m and, therefore, can vary by a factor of about four. Thinning of the permafrost from the Prudhoe Bay area toward the foothills of the Brooks Range appears to be caused by the changing geology (through its effect on the thermal conductivity of the rocks) and the increase in mean annual ground surface temperature with distance from the coast. In the offshore area toward Reindeer Island, relatively simple models explain and give reasonable predictions for thawing of the ice-bearing subsea permafrost at the sea bed and for thawing at its base.

Smectite Diagenesis in Bentonites of Shale Wall Member of Seabee Formation, North Slope, Alaska: ABSTRACT

The Upper Cretaceous Colville Group is present over much of the north-central North Slope and includes the Seabee Formation, a part of a progradational clastic wedge derived from the ancestral Brooks Range. The lower member of the Seabee Formation, the Shale Wall Member, contains thin to moderately thick bentonite beds. Biotite separated from bentonite from the Shale Wall Member in the northwestern subcrop area yielded K/Ar ages of about 92 Ma, dating the origin of these pyroclastic deposits as early Turonian. In the northern part of the National Petroleum Reserve in Alaska (NPRA) and in the vicinity of Prudhoe Bay field, the less than 2-millimicron fraction of Shale Wall bentonites consists predominantly of smectite with trace to minor amounts of kaolinite. Eastward alon the Barrow arch, the depth of burial of the Shale Wall Member increases from less than 300 m in the NPRA to at least 3,855 m in the vicinity of Mikkelsen Bay as a result of downwarping of the Barrow arch and thick Tertiary deposition. At a depth of burial of about 3,600 m, the smectite-rich bentonites are replaced by rectorite, an ordered mixed-layer illite/smectite (I/S). With increasing depth of burial, the percentage of expandable layers in the ordered I/S decreases from about 45% to 20%. K/Ar dating of the ordered I/S phase places the time of formation in the mid-Miocene, in close agreement with predicted timing of clay diagenesis based on burial history/thermal gradient considerations. End_of_Article - Last_Page 665------------