Strontium isotopes reveal diverse life history variations, migration patterns, and habitat use for Broad Whitefish (Coregonus nasus) in Arctic, Alaska

Conservation of Arctic fish species is challenging partly due to our limited ability to track fish through time and space, which constrains our understanding of life history diversity and lifelong habitat use. Broad Whitefish ( Coregonus nasus ) is an important subsistence species for Alaska’s Arctic Indigenous communities, yet little is known about life history diversity, migration patterns, and freshwater habitat use. Using laser ablation Sr isotope otolith microchemistry, we analyzed Colville River Broad Whitefish 87 Sr/ 86 Sr chronologies (n = 61) to reconstruct movements and habitat use across the lives of individual fish. We found evidence of at least six life history types, including three anadromous types, one semi-anadromous type, and two nonanadromous types. Anadromous life history types comprised a large proportion of individuals sampled (collectively, 59%) and most of these (59%) migrated to sea between ages 0–2 and spent varying durations at sea. The semi-anadromous life history type comprised 28% of samples and entered marine habitat as larvae. Nonanadromous life history types comprised the remainder (collectively, 13%). Otolith 87 Sr/ 86 Sr data from juvenile and adult freshwater stages suggest that habitat use changed in association with age, seasons, and life history strategies. This information on Broad Whitefish life histories and habitat use across time and space will help managers and conservation planners better understand the risks of anthropogenic impacts and help conserve this vital subsistence resource.

Ulungarat Basin: Record of a major Middle Devonian to Mississippian syn-rift to post-rift tectonic transition, eastern Brooks Range, Arctic Alaska

The Ulungarat Basin of Arctic Alaska is a unique exposed stratigraphic record of the mid-Paleozoic transition from the Romanzof orogeny to post-orogenic rifting and Ellesmerian passive margin subsidence. The Ulungarat Basin succession is composed of both syn-rift and post-rift deposits recording this mid-Paleozoic transition. The syn-rift deposits unconformably overlie highly deformed Romanzof orogenic basement on the mid-Paleozoic regional angular unconformity and are unconformably overlain by post-rift Endicott Group deposits of the Ellesmerian passive margin. Shallow marine strata of Eifelian age at the base of the Ulungarat Formation record onset of rifting and limit age of the Romanzof orogeny to late Early Devonian. Abrupt thickness and facies changes within the Ulungarat Formation and disconformably overlying syn-rift Mangaqtaaq Formation suggest active normal faulting during deposition. The Mangaqtaaq Formation records lacustrine deposition in a restricted down-faulted structural low. The unconformity between syn-rift deposits and overlying post-rift Endicott Group is interpreted to be the result of sediment bypass during deposition of the outboard allochthonous Endicott Group. Within Ulungarat Basin, transgressive post-rift Lower Mississippian Kekiktuk Conglomerate and Kayak Shale (Endicott Group) are older and thicker than equivalents to the north. North of Ulungarat Basin, deformed pre-Middle Devonian rocks were exposed to erosion at the mid-Paleozoic regional uncon­formity for ~50 m.y., supplying sediments to the rift basin and broader Arctic Alaska rifted margin beyond. Although Middle Devonian to Lower Mississip­pian chert- and quartz-pebble conglomerates and sandstones across Arctic Alaska share a common provenance from the eroding ancestral Romanzof highlands, they were deposited in different tectonic settings.

Supplemental Material: Ulungarat Basin: Record of a major Middle Devonian to Mississippian syn-rift to post-rift tectonic transition, eastern Brooks Range, Arctic Alaska

<div>Describes the organization, sedimentology, and depositional environments of the Ulungarat Basin succession including description of type sections of the Ulungarat and Mangaqtaaq formations. Table S1 documents published fossil and radiometric age constraints used to construct the mid-Paleozoic tectonostratigraphic chart (Fig. 12), including basis for age assignment and list of source references. A reference list of all sources cited in Table S1 is included.<br></div>

Arctic Alaska Basin, Hanna Trough, and Beaufortian Rifted Margin Composite Tectono-Sedimentary Elements

The Arctic Alaska region includes three composite tectono-sedimentary elements (CTSEs): the (1) Arctic Alaska Basin (AAB), (2) Hanna Trough (HT), and (3) Beaufortian Rifted Margin (BRM) CTSEs. These CTSEs comprise Mississippian to Lower Cretaceous (Neocomian) strata beneath much of the Alaska North Slope, the Chukchi Sea and westernmost North Slope, and Beaufort Sea, respectively. These sedimentary successions rest on Devonian and older sedimentary and metasedimentary rocks, considered economic basement, and are overlain by Cretaceous to Cenozoic syn- and post-tectonic strata deposited in the foreland of the Chukotka and Brooks Range orogens and in the Amerasia Basin. (1) The Mississippian-Neocomian AAB CTSE includes two TSEs: (a) The Ellesmerian Platform TSE comprises mainly shelf strata of Mississippian to Middle Jurassic age and includes a relatively undeformed domain in the north and a fold-and-thrust domain in the south. (b) The Beaufortian Rift Shoulder TSE includes Middle Jurassic to Neocomian deposits related to rift-shoulder uplift. (2) The HT CTSE includes four TSEs: (a) The Ellesmerian Syn-Rift TSE comprises Late Devonian(?) to Middle Mississippian growth strata deposited in grabens and half grabens during intracontinental rifting. (b) The Ellesmerian-Beaufortian Sag-Basin TSE comprises Middle Mississippian to Upper Triassic strata deposited in a sag basin following cessation of rifting. (c) The Beaufortian Syn-Rift TSE comprises Jurassic to Neocomian graben-fill deposits related to rifting in the Amerasia and North Chukchi Basins. (d) The Beaufortian Rift-Shoulder TSE comprises Jurassic to Neocomian strata related to rifting and deposited outside rift basins. (3) The BRM CTSE includes two TSEs: (a) The Beaufortian Syn-Rift TSE comprises Middle Jurassic to Neocomian syn-rift strata deposited on attenuated continental crust associated with opening of the Amerasia Basin. (b) The Ellesmerian Platform TSE comprises mainly shelf strata of Mississippian to Middle Jurassic age that lie beneath Beaufortian syn-rift strata.The AAB, HT, and BRM CTSEs contain oil-prone source rocks in Triassic, Jurassic, and Cretaceous strata and proven reservoir rocks spanning Mississippian to Lower Cretaceous strata. A structurally high-standing area in the northern AAB CTSE, northern HT CTSE, and southernmost BRM CTSE lies in the oil window whereas all other areas lie in the gas window. Known hydrocarbon accumulations in the three CTSEs total more than 30 billion barrels of oil equivalent and yet-to-find estimates suggest a similar volume remains to be discovered.

Quantifying effects of snow depth on caribou winter range selection and movement in Arctic Alaska

Background Caribou and reindeer across the Arctic spend more than two thirds of their lives moving in snow. Yet snow-specific mechanisms driving their winter ecology and potentially influencing herd health and movement patterns are not well known. Integrative research coupling snow and wildlife sciences using observations, models, and wildlife tracking technologies can help fill this knowledge void. Methods Here, we quantified the effects of snow depth on caribou winter range selection and movement. We used location data of Central Arctic Herd (CAH) caribou in Arctic Alaska collected from 2014 to 2020 and spatially distributed and temporally evolving snow depth data produced by SnowModel. These landscape-scale (90 m), daily snow depth data reproduced the observed spatial snow-depth variability across typical areal extents occupied by a wintering caribou during a 24-h period. Results We found that fall snow depths encountered by the herd north of the Brooks Range exerted a strong influence on selection of two distinct winter range locations. In winters with relatively shallow fall snow depth (2016/17, 2018/19, and 2019/20), the majority of the CAH wintered on the tundra north of the Brooks Range mountains. In contrast, during the winters with relatively deep fall snow depth (2014/15, 2015/16, and 2017/18), the majority of the CAH caribou wintered in the mountainous boreal forest south of the Brooks Range. Long-term (19 winters; 2001–2020) monitoring of CAH caribou winter distributions confirmed this relationship. Additionally, snow depth affected movement and selection differently within these two habitats: in the mountainous boreal forest, caribou avoided areas with deeper snow, but when on the tundra, snow depth did not trigger significant deep-snow avoidance. In both wintering habitats, CAH caribou selected areas with higher lichen abundance, and they moved significantly slower when encountering deeper snow. Conclusions In general, our findings indicate that regional-scale selection of winter range is influenced by snow depth at or prior to fall migration. During winter, daily decision-making within the winter range is driven largely by snow depth. This integrative approach of coupling snow and wildlife observations with snow-evolution and caribou-movement modeling to quantify the multi-facetted effects of snow on wildlife ecology is applicable to caribou and reindeer herds throughout the Arctic.

Supplemental Material: Ulungarat Basin: Record of a major Middle Devonian to Mississippian syn-rift to post-rift tectonic transition, eastern Brooks Range, Arctic Alaska

<div>Describes the organization, sedimentology, and depositional environments of the Ulungarat Basin succession including description of type sections of the Ulungarat and Mangaqtaaq formations. Table S1 documents published fossil and radiometric age constraints used to construct the mid-Paleozoic tectonostratigraphic chart (Fig. 12), including basis for age assignment and list of source references. A reference list of all sources cited in Table S1 is included.<br></div>

A pulse of mercury and major ions in snowmelt runoff from a small Arctic Alaska watershed

Atmospheric mercury (Hg) is deposited to Polar Regions during springtime atmospheric mercury depletion events (AMDEs) that require halogens and snow or ice surfaces. The fate of this Hg during and following snowmelt is largely unknown. We measured Hg, major ions, and stable water isotopes from the snowpack through the entire spring melt runoff period for two years. Our small (2.5 ha) watershed is near Barrow (now Utqiaġvik), Alaska. We measured discharge, made 10 000 snow depths, and collected over 100 samples of snow and meltwater for chemical analysis in 2008 and 2009 from the watershed snowpack and ephemeral stream channel. Our results suggest AMDE Hg complexed with Cl⁻ or Br⁻ may be less likely to be photochemically reduced and re-emitted to the atmosphere prior to snowmelt, and we estimate that roughly 25% of the Hg in snowmelt is attributable to AMDEs. Projected Arctic warming, with more open sea ice leads providing halogen sources that promote AMDEs, may provide enhanced Hg deposition, reduced Hg emission and, ultimately, an increase in snowpack and snowmelt runoff Hg concentrations.

Reply to Blair

Blair provides a thorough review of data he claims stands in opposition to our narrative concerning the origins of IIa40/Early Blue glass trade beads and their presence in arctic Alaska prior to Columbus’ initial voyage. He employs three lines of evidence: historical and archaeological data, Instrumental Neutron Activation Analysis, and radiocarbon dating. Our reply addresses his application of these data sets, clarifying his use of our data to arrive at his conclusions. While we continue to disagree with Blair, we do wish to acknowledge his time spent on debating the issue thereby furthering all of our understanding on this topic.