Mechanisms and implications of changes in the timing of ocean freeze-up

Thesis (Ph.D.) University of Alaska Fairbanks, 2018The shift to an Arctic seasonal sea ice cover in recent years motivates a deeper understanding of freeze-up processes and implications of a lengthened open water season. As the sea ice boundary between the Arctic ocean and atmosphere covers a smaller area, the effects of enhanced wind mixing become more pronounced. Winds are important for ocean circulation and heat exchange. Ultimately, they can influence when freeze-up can occur, or can break up new ice as it forms. The chapters of this thesis are motivated by the substantial social and geophysical consequences of a lengthening open water season and linked through discussion of what controls freeze-up timing. Implications of a declining sea ice cover as it pertains to the three Arctic Alaska coastal communities of Kotzebue, Shishmaref, and Utqiaġvik are explored in depth. Indices of locally-relevant metrics are developed by using physical climate-related thresholds found by other studies to impact Alaska communities and coastal erosion rates. This allows for a large-scale climate dataset to be used to define a timeseries of these indices for each community. We found a marked increase in the number of false freeze-ups and break-ups, the number of days too windy to hunt via subsistence boat, and in Utqiaġvik, an approximate tripling of erosion-capable wind events from 1979-2014. The WRF-downscaled ERA-Interim dataset (ERA-Interim for sea ice) was also used in the analysis of all chapters. The cumulative wind energy input into the upper ocean was calculated for the Chukchi, southern Beaufort, and northeast Bering Seas at time periods up to three months prior to freeze-up, and then correlated with the timing of freeze-up. We have found that increased wind energy input into the upper ocean 2-3 months prior to freeze-up is positively and most strongly correlated with the date of freeze-up in the Chukchi Sea. Analysis of wind climatology shows winds are increasing in the period prior to freeze-up as a delayed freeze-up moves into the fall storm season. A negative correlation is found in the Bering Sea over shorter timescales, suggesting that storms promote the arrival of sea ice there. Case studies are evaluated for the Chukchi Sea and Bering Sea, to illustrate mechanisms at play that cause the positive and negative correlations in these seas, respectively. Ice advection and high winds from northerly directions are shown to hasten the timing of freeze-up in the Bering Sea. In the Chukchi Sea, higher winds from the dominant northeasterly direction promote upwelling of warm and salty water up onto the shelf, which suggests a mechanism for why high winds are associated with a delayed freeze-up there. We next examine the effect of winds on freeze-up timing by using a 1-D vertical column model of the mixed layer. The model is initialized using temperature and salinity profiles obtained from a freeze-up buoy deployed in 2015 in the north-east part of the Chukchi Sea. The meteorological forcing used to drive the model experiments comes from a WRF-downscaled ERA-Interim Reanalysis dataset. Our results show that vertical wind-driven mixing leads to enhanced heat loss. In light of the previously found positive correlation between wind energy input and freeze-up timing, the mixing model results suggest horizontal advection not captured by the 1-D column model can dominate wind-driven vertical mixing to promote freeze-up.ArcSEES NSF award 1263853, Center for Global Chang

Drivers of Turbidity and Its Seasonal Variability at Herschel Island Qikiqtaruk (Western Canadian Arctic)

The Arctic is greatly affected by climate change. Increasing air temperatures drive permafrost thaw and an increase in coastal erosion and river discharge. This results in a greater input of sediment and organic matter into nearshore waters, impacting ecosystems by reducing light transmission through the water column and altering biogeochemistry. This potentially results in impacts on the subsistence economy of local people as well as the climate due to the transformation of suspended organic matter into greenhouse gases. Even though the impacts of increased suspended sediment concentrations and turbidity in the Arctic nearshore zone are well-studied, the mechanisms underpinning this increase are largely unknown. Wave energy and tides drive the level of turbidity in the temperate and tropical parts of the world, and this is generally assumed to also be the case in the Arctic. However, the tidal range is considerably lower in the Arctic, and processes related to the occurrence of permafrost have the potential to greatly contribute to nearshore turbidity. In this study, we use high-resolution satellite imagery alongside in situ and ERA5 reanalysis data of ocean and climate variables in order to identify the drivers of nearshore turbidity, along with its seasonality in the nearshore waters of Herschel Island Qikiqtaruk, in the western Canadian Arctic. Nearshore turbidity correlates well to wind direction, wind speed, significant wave height, and wave period. Nearshore turbidity is superiorly correlated to wind speed at the Beaufort Shelf compared to in situ measurements at Herschel Island Qikiqtaruk, showing that nearshore turbidity, albeit being of limited spatial extent, is influenced by large-scale weather and ocean phenomenons. We show that, in contrast to the temperate and tropical ocean, freshly eroded material is the predominant driver of nearshore turbidity in the Arctic, rather than resuspension, which is caused by the vulnerability of permafrost coasts to thermo-erosion

ArcticBeach v1.0: A physics-based parameterization of pan-Arctic coastline erosion

In the Arctic, air temperatures are increasing and sea ice is declining, resulting in larger waves and a longer open water season, all of which intensify the thaw and erosion of ice-rich coasts. Climate change has been shown to increase the rate of Arctic coastal erosion, causing problems for Arctic cultural heritage, existing industrial, military, and civil infrastructure, as well as changes in nearshore biogeochemistry. Numerical models that reproduce historical and project future Arctic erosion rates are necessary to understand how further climate change will affect these problems, and no such model yet exists to simulate the physics of erosion on a pan-Arctic scale. We have coupled a bathystrophic storm surge model to a simplified physical erosion model of a permafrost coastline. This Arctic erosion model, called ArcticBeach v1.0, is a first step toward a physical parameterization of Arctic shoreline erosion for larger-scale models. It is forced by wind speed and direction, wave period and height, sea surface temperature, all of which are masked during times of sea ice cover near the coastline. Model tuning requires observed historical retreat rates (at least one value), as well as rough nearshore bathymetry. These parameters are already available on a pan-Arctic scale. The model is validated at three study sites at 1) Drew Point (DP), Alaska, 2) Mamontovy Khayata (MK), Siberia, and 3) Veslebogen Cliffs, Svalbard. Simulated cumulative retreat rates for DP and MK respectively (169 and 170 m) over the time periods studied at each site (2007–2016, and 1995–2018) are found to the same order of magnitude as observed cumulative retreat (172 and 120 m). The rocky Veslebogen cliffs have small observed cumulative retreat rates (0.05 m over 2014–2016), and our model was also able to reproduce this same order of magnitude of retreat (0.08 m). Given the large differences in geomorphology between the study sites, this study provides a proof-of-concept that ArcticBeach v1.0 can be applied on very different permafrost coastlines. ArcticBeach v1.0 provides a promising starting point to project retreat of Arctic shorelines, or to evaluate historical retreat in places that have had few observations.Peer Reviewe

Sea ice concentration data produced from a simulation with the sea ice model CICE-CPOM-2019, including a prognostic floe size distribution model to study the Marginal Ice Zone

Monthly mean sea ice concentration output from CICE-CPOM-2019, a stand-alone (fully forced) dynamic-thermodynamic sea ice model, based on CICE model version 5.1.2, but with an added prognostic floe-size distribution, prognostic melt pond model, elastic anisotropic plastic rheology, and a prognostic ocean mixed layer. Details on the forcing and full references concerning the modifications made to the original CICE model can be found in the Readme file

Changes of the Arctic marginal ice zone during the satellite era

Many studies have shown a decrease in Arctic sea ice extent. It does not logically follow, however, that the extent of the marginal ice zone (MIZ), here defined as the area of the ocean with ice concentrations from 15 to 80%, is also changing. Changes in the MIZ extent has implications for the level of atmospheric and ocean heat and gas exchange in the area of partially ice-covered ocean, as well as for the extent of habitat for organisms that rely on the MIZ, from primary producers like sea ice algae to seals and birds. Here, we present, for the first time, an analysis of satellite observations of pan-Arctic averaged MIZ extent. We find no trend in the MIZ extent during the last 40 years from observations. Our results indicate that the constancy of the MIZ extent is the result of an observed increase in width of the MIZ being compensated by a decrease in the perimeter of the MIZ as it moves further north. We present simulations from a coupled sea ice-ocean mixed layer model using a prognostic floe size distribution which we find is consistent with, but poorly constrained by, existing satellite observations of pan-Arctic MIZ extent. We provide seasonal upper and lower bounds on MIZ extent based on the 4 satellite-derived sea ice concentration datasets used. We find a large and significant increase (>50%) in the August and September MIZ fraction (MIZ extent divided by sea ice extent) for the Bootstrap and OSI-450 observational datasets, which can be attributed to the reduction in total sea ice extent. Given the results of this study, we suggest that references to ‘rapid changes’ in the MIZ should remain cautious and provide a specific and clear definition of both the MIZ itself and also the property of the MIZ that is changing

Returning home: heritage work among the Stl'atl'imx of the Lower Lillooet River Valley

This article focusses on heritage practices in the tensioned landscape of the Stl’atl’imx (pronounced Stat-lee-um) people of the Lower Lillooet River Valley, British Columbia, Canada. Displaced from their traditional territories and cultural traditions through the colonial encounter, they are enacting, challenging and remaking their heritage as part of their long term goal to reclaim their land and return ‘home’. I draw on three examples of their heritage work: graveyard cleaning, the shifting ‘official’/‘unofficial’ heritage of a wagon road, and marshalling of the mountain named Nsvq’ts (pronounced In-SHUCK-ch) in order to illustrate how the past is strategically mobilised in order to substantiate positions in the present. While this paper focusses on heritage in an Indigenous and postcolonial context, I contend that the dynamics of heritage practices outlined here are applicable to all heritage practices

A pan-Arctic initiative on the spatial and temporal dynamics of Arctic coasts

Permafrost coasts make up roughly one third of all coasts worldwide. Their erosion leads to the release of previously locked organic carbon, changes in ecosystems and the destruction of cultural heritage, infrastructure and whole communities. Since rapid environmental changes lead to an intensification of Arctic coastal dynamics, it is of great importance to adequately quantify current and future coastal changes. However, the remoteness of the Arctic and scarcity of data limit our understanding of coastal dynamics at a pan-Arctic scale and prohibit us from getting a complete picture of the diversity of impacts on the human and natural environment. In a joint effort of the EU project NUNATARYUK and the NSF project PerCS-Net, we seek to close this knowledge gap by collecting and analyzing all accessible high-resolution shoreline position data for the Arctic coastline. These datasets include geographical coordinates combined with coastal positions derived from archived data, surveying data, air and space born remote sensing products, or LiDAR products. The compilation of this unique dataset will enable us to reach unprecedented data coverage and will allow us a first insight into the magnitude and trends of shoreline changes on a pan-Arctic scale with locally highly resolved temporal and spatial changes in shoreline dynamics. By comparing consistently derived shoreline change data from all over the Arctic we expect that the trajectory of coastal change in the Arctic becomes evident. A synthesis of some initial results will be presented in the 2020 Arctic Report Card on Arctic Coastal Dynamics. This initiative is an ongoing effort – new data contributions are welcome

Evidence for 28 genetic disorders discovered by combining healthcare and research data

De novo mutations in protein-coding genes are a well-established cause of developmental disorders. However, genes known to be associated with developmental disorders account for only a minority of the observed excess of such de novo mutations. Here, to identify previously undescribed genes associated with developmental disorders, we integrate healthcare and research exome-sequence data from 31,058 parent–offspring trios of individuals with developmental disorders, and develop a simulation-based statistical test to identify gene-specific enrichment of de novo mutations. We identified 285 genes that were significantly associated with developmental disorders, including 28 that had not previously been robustly associated with developmental disorders. Although we detected more genes associated with developmental disorders, much of the excess of de novo mutations in protein-coding genes remains unaccounted for. Modelling suggests that more than 1,000 genes associated with developmental disorders have not yet been described, many of which are likely to be less penetrant than the currently known genes. Research access to clinical diagnostic datasets will be critical for completing the map of genes associated with developmental disorders

Heterozygous ANKRD17 loss-of-function variants cause a syndrome with intellectual disability, speech delay, and dysmorphism

ANKRD17 is an ankyrin repeat-containing protein thought to play a role in cell cycle progression, whose ortholog in Drosophila functions in the Hippo pathway as a co-factor of Yorkie. Here, we delineate a neurodevelopmental disorder caused by de novo heterozygous ANKRD17 variants. The mutational spectrum of this cohort of 34 individuals from 32 families is highly suggestive of haploinsufficiency as the underlying mechanism of disease, with 21 truncating or essential splice site variants, 9 missense variants, 1 in-frame insertion-deletion, and 1 microdeletion (1.16 Mb). Consequently, our data indicate that loss of ANKRD17 is likely the main cause of phenotypes previously associated with large multi-gene chromosomal aberrations of the 4q13.3 region. Protein modeling suggests that most of the missense variants disrupt the stability of the ankyrin repeats through alteration of core structural residues. The major phenotypic characteristic of our cohort is a variable degree of developmental delay/intellectual disability, particularly affecting speech, while additional features include growth failure, feeding difficulties, non-specific MRI abnormalities, epilepsy and/or abnormal EEG, predisposition to recurrent infections (mostly bacterial), ophthalmological abnormalities, gait/balance disturbance, and joint hypermobility. Moreover, many individuals shared similar dysmorphic facial features. Analysis of single-cell RNA-seq data from the developing human telencephalon indicated ANKRD17 expression at multiple stages of neurogenesis, adding further evidence to the assertion that damaging ANKRD17 variants cause a neurodevelopmental disorder

Mice Deficient in GEM GTPase Show Abnormal Glucose Homeostasis Due to Defects in Beta-Cell Calcium Handling

Glucose-stimulated insulin secretion from beta-cells is a tightly regulated process that requires calcium flux to trigger exocytosis of insulin-containing vesicles. Regulation of calcium handling in beta-cells remains incompletely understood. Gem, a member of the RGK (Rad/Gem/Kir) family regulates calcium channel handling in other cell types, and Gem over-expression inhibits insulin release in insulin-secreting Min6 cells. The aim of this study was to explore the role of Gem in insulin secretion. We hypothesised that Gem may regulate insulin secretion and thus affect glucose tolerance in vivo