Response of major modes of eastern Arctic Ocean variability to climate change

Thesis (Ph.D.) University of Alaska Fairbanks, 2019The Arctic Ocean plays a central role in ongoing climate change, with sea ice loss being the most prominent indicator. Recent observations showed that Atlantic inflows play an increasingly important role in the demise of sea ice. This encroaching atlantification of the eastern Arctic Ocean impacts the mean state and the variability of hydrography and current dynamics throughout the basin. Among the most energetic modes of variability are the seasonal cycle and high frequency semidiurnal (∼12-hourly) dynamics in the tidal and inertial frequency band. Limited observations indicated a substantial increase of both, hydrographic seasonal cycles as well as semidiurnal current dynamics in the eastern Arctic over the last decade. Using a uniquely comprehensive data set from an array of six moorings deployed across the eastern Eurasian Basin (EB) continental slope along the 125°E meridian between 2013 and 2015 within the NABOS project, we assess the state of hydrographic seasonal cycles in the eastern EB. Results show a complex pattern of seasonality with a remarkably strong (∆T=1.4°C), deep reaching (∼600 m) temperature signal over the continental slope and large-scale seasonal displacements of isopycnal interfaces. Seasonally changing background conditions are also the main source of variability of semidiurnal frequency band currents: During winter, vigorous baroclinic tidal currents whose amplitudes by far exceed predictions follow the vertical evolution of the pycnocline. During summer, extensive open-water periods additionally lead to strong wind-driven inertial currents in the upper ocean, routinely exceeding 30 cm/s far offshore in the deep basin. In order to obtain an Arctic-wide perspective on the impact of baroclinic tidal currents, a pan-Arctic tidal current atlas has been developed that synthesizes all available observations from the last 20 years. This atlas allows for in-depth studies of regional baroclinic tidal current variability as well as for validation of ocean and climate models, an essential step towards more accurate projections of the future Arctic Ocean state. Our findings from the eastern EB region already indicate a new, more dynamic state of the eastern Arctic Ocean with direct implications for the ecosystem and further sea-ice reduction

Field-test of a robust, portable, frequency-stable laser

We operate a frequency-stable laser in a non-laboratory environment where the test platform is a passenger vehicle. We measure the acceleration experienced by the laser and actively correct for it to achieve a system acceleration sensitivity of $\Delta f / f$ = $11(2) \times 10^{-12}$/g, $6(2) \times 10^{-12}$/g, and $4(1) \times 10^{-12}$/g for accelerations in three orthogonal directions at 1 Hz. The acceleration spectrum and laser performance are evaluated with the vehicle both stationary and moving. The laser linewidth in the stationary vehicle with engine idling is 1.7(1) Hz

Eddies and the distribution of Eddy Kinetic Energy in the Arctic Ocean

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in von Appen, W.-J., Baumann, T. M., Janout, M., Koldunov, N., Lenn, Y.-D., Pickart, R. S., Scott, R. B., & Wang, Q. Eddies and the distribution of eddy kinetic energy in the Arctic Ocean. Oceanography, 35(2), (2022), https://doi.org/10.5670/oceanog.2022.122.Mesoscale eddies are important to many aspects of the dynamics of the Arctic Ocean. Among others, they maintain the halocline and interact with the Atlantic Water circumpolar boundary current through lateral eddy fluxes and shelf-basin exchanges. Mesoscale eddies are also important for transporting biological material and for modifying sea ice distribution. Here, we review what is known about eddies and their impacts in the Arctic Ocean in the context of rapid climate change. Eddy kinetic energy (EKE) is a proxy for mesoscale variability in the ocean due to eddies. We present the first quantification of EKE from moored observations across the entire Arctic Ocean and compare those results to output from an eddy resolving numerical model. We show that EKE is largest in the northern Nordic Seas/Fram Strait and it is also elevated along the shelf break of the Arctic Circumpolar Boundary Current, especially in the Beaufort Sea. In the central basins, EKE is 100–1,000 times lower. Generally, EKE is stronger when sea ice concentration is low versus times of dense ice cover. As sea ice declines, we anticipate that areas in the Arctic Ocean where conditions typical of the North Atlantic and North Pacific prevail will increase. We conclude that the future Arctic Ocean will feature more energetic mesoscale variability

Intensification of Near-Surface Currents and Shear in the Eastern Arctic Ocean:A More Dynamic Eastern Arctic Ocean

A 15-year (2004–2018) record of mooring observations from the upper 50 m of the ocean in the eastern Eurasian Basin reveals increased current speeds and vertical shear, associated with an increasing coupling between wind, ice, and the upper ocean over 2004–2018, particularly in summer. Substantial increases in current speeds and shears in the upper 50 m are dominated by a two times amplification of currents in the semidiurnal band, which includes tides and wind-forced near-inertial oscillations. For the first time the strengthened upper ocean currents and shear are observed to coincide with weakening stratification. This coupling links the Atlantic Water heat to the sea ice, a consequence of which would be reducing regional sea ice volume. These results point to a new positive feedback mechanism in which reduced sea ice extent facilitates more energetic inertial oscillations and associated upper-ocean shear, thus leading to enhanced ventilation of the Atlantic Water

Overview of the MOSAiC expedition: Physical oceanography

Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present along-drift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling capabilities in the Arctic Ocean.publishedVersio

Weakening of cold halocline layer exposes sea ice to oceanic heat in the eastern Arctic Ocean

A 15-yr duration record of mooring observations from the eastern (>70°E) Eurasian Basin (EB) of the Arctic Ocean is used to show and quantify the recently increased oceanic heat flux from intermediate-depth (~150–900 m) warm Atlantic Water (AW) to the surface mixed layer and sea ice. The upward release of AW heat is regulated by the stability of the overlying halocline, which we show has weakened substantially in recent years. Shoaling of the AW has also contributed, with observations in winter 2017–18 showing AW at only 80 m depth, just below the wintertime surface mixed layer, the shallowest in our mooring records. The weakening of the halocline for several months at this time implies that AW heat was linked to winter convection associated with brine rejection during sea ice formation. This resulted in a substantial increase of upward oceanic heat flux during the winter season, from an average of 3–4 W m−2 in 2007–08 to >10 W m−2 in 2016–18. This seasonal AW heat loss in the eastern EB is equivalent to a more than a twofold reduction of winter ice growth. These changes imply a positive feedback as reduced sea ice cover permits increased mixing, augmenting the summer-dominated ice-albedo feedback

On the seasonal cycles observed at the continental slope of the Eastern Eurasian Basin of the Arctic Ocean

The Eurasian Basin (EB) of the Arctic Ocean is subject to substantial seasonality. We here use data collected between 2013 and 2015 from six moorings across the continental slope in the eastern EB and identify three domains, each with its own unique seasonal cycle: 1) The upper ocean (<100 m), with seasonal temperature and salinity differences of Δθ = 0.16°C and ΔS = 0.17, is chiefly driven by the seasonal sea ice cycle. 2) The upper-slope domain is characterized by the influence of a hydrographic front that spans the water column around the ~750-m isobath. The domain features a strong temperature and moderate salinity seasonality (Δθ = 1.4°C; ΔS = 0.06), which is traceable down to ~600-m depth. Probable cause of this signal is a combination of along-slope advection of signals by the Arctic Circumpolar Boundary Current, local wind-driven upwelling, and a cross-slope shift of the front. 3) The lower-slope domain, located offshore of the front, with seasonality in temperature and salinity mainly confined to the halocline (Δθ = 0.83°C; ΔS = 0.11; ~100–200 m). This seasonal cycle can be explained by a vertical isopycnal displacement (ΔZ ~ 36 m), arguably as a baroclinic response to sea level changes. Available long-term oceanographic records indicate a recent amplification of the seasonal cycle within the halocline layer, possibly associated with the erosion of the halocline. This reduces the halocline’s ability to isolate the ocean surface layer and sea ice from the underlying Atlantic Water heat with direct implications for the evolution of Arctic sea ice cover and climate

The Testing by Fire of the Builders' Works: 1 Corinthians 3.10-15

Wetensch. publicati

Overview of the MOSAiC expedition: Physical oceanography

Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. An international team designed and implemented the program to characterize the Arctic Ocean system in unprecedented detail, from the seafloor to the air-sea ice-ocean interface, from sub-mesoscales to pan-Arctic. The oceanographic measurements were coordinated with the other teams to explore the ocean physics and linkages to the climate and ecosystem. This paper introduces the major components of the physical oceanography program and complements the other team overviews of the MOSAiC observational program. Team OCEAN’s sampling strategy was designed around hydrographic ship-, ice- and autonomous platform-based measurements to improve the understanding of regional circulation and mixing processes. Measurements were carried out both routinely, with a regular schedule, and in response to storms or opening leads. Here we present along-drift time series of hydrographic properties, allowing insights into the seasonal and regional evolution of the water column from winter in the Laptev Sea to early summer in Fram Strait: freshening of the surface, deepening of the mixed layer, increase in temperature and salinity of the Atlantic Water. We also highlight the presence of Canada Basin deep water intrusions and a surface meltwater layer in leads. MOSAiC most likely was the most comprehensive program ever conducted over the ice-covered Arctic Ocean. While data analysis and interpretation are ongoing, the acquired datasets will support a wide range of physical oceanography and multi-disciplinary research. They will provide a significant foundation for assessing and advancing modeling capabilities in the Arctic Ocean