Michael J Karcher

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• Dr.
• Researcher at Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Fram Strait is one of the main gateways for fresh water leaving the Arctic Ocean toward the deep‐water formation regions of the North Atlantic. Monitoring transport through Fram Strait is important to quantify the impact of Arctic amplification on the hydrography in lower latitudes. We update existing time series from the moorings in the western Fr...

The potential for contamination was studied for several hypothetical scenarios where radioactivity was released from the floating nuclear power plant Akademik Lomonosov.

As Arctic sea ice deteriorates, more light enters the ocean, causing largely unknown effects on the ecosystem. Using an autonomous biophysical observatory, we recorded zooplankton vertical distribution under Arctic sea ice from dusk to dawn of the polar night. Here we show that zooplankton ascend into the under-ice habitat during autumn twilight, f...

Arctic Ocean gateway fluxes play a crucial role in linking the Arctic with the global ocean and affecting climate and marine ecosystems. We reviewed past studies on Arctic–Subarctic ocean linkages and examined their changes and driving mechanisms. Our review highlights that radical changes occurred in the inflows and outflows of the Arctic Ocean du...

As Arctic sea ice deteriorates, more light enters the Arctic Ocean, causing largely unknown effects on the ecosystem. A novel autonomous bio-physical observatory provided the first record of zooplankton vertical distribution under sea ice drifting across the Arctic Ocean from dusk to dawn of the polar night. Its measurements revealed that zooplankt...

The Arctic is no longer a region dominated by thick multi-year ice (MYI), but by thinner, more dynamic, first-year-ice (FYI). This shift towards a seasonal ice cover has consequences for the under-ice light field, as sea-ice and its snow cover are a major factor influencing radiative transfer and thus, biological activity within- and under the ice....

Arctic observing and data systems have been widely recognized as critical infrastructures to support decision making and understanding across sectors in the Arctic and globally. Yet due to broad and persistent issues related to coordination, deployment infrastructure and technology gaps, the Arctic remains among the most poorly observed regions on...

The Arctic marine ecosystem is shaped by the seasonality of the solar cycle, spanning from 24-h light at the sea surface in summer to 24-h darkness in winter. The amount of light available for under-ice ecosystems is the result of different physical and biological processes that affect its path through atmosphere, snow, sea ice and water. In this a...

I measurements on samples collected during GEOTRACES oceanographic missions in the Arctic Ocean in 2015 have provided the first synoptic ¹²⁹I sections across the Eurasian, Canada, and Makarov Basins. During the 1990s, increased discharges of ¹²⁹I from European nuclear fuel reprocessing plants produced a large, tracer spike whose passage through the...

Arctic sea ice is shifting from a year-round to a seasonal sea ice cover. This substantial transformation, via a reduction in Arctic sea ice extent and a thinning of its thickness, influences the amount of light entering the upper ocean. This in turn impacts under-ice algal growth and associated ecosystem dynamics. Field campaigns have provided val...

When the air is very cold, water at the surface of the ocean freezes, forming sea ice. Parts of the Arctic Ocean are covered by sea ice during the entire year. Often, snow falls onto the sea ice. Despite the cold, many plants and animals can live in the Arctic Ocean, some in the water, and some even in the sea ice. Particularly, algae can live in s...

In September 2019, the research icebreaker Polarstern started the largest multidisciplinary Arctic expedition to date, the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) drift experiment. Being moored to an ice floe for a whole year, thus including the winter season, the declared goal of the expedition is to better...

In September 2019, the research icebreaker Polarstern started the largest multidisciplinary Arctic expedition so far, the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) drift experiment. Being moored to an ice floe for a whole year, thus including the winter season, the declared goal of the expedition is to better u...

The uniqueness of optimal parameter sets of an Arctic sea ice simulation is investigated. A set of parameter optimization experiments is performed using an automatic parameter optimization system, which simultaneously optimizes 15 dynamic and thermodynamic process parameters. The system employs a stochastic approach (genetic algorithm) to find the...

Improvement and optimization of numerical sea ice models are of great relevance for understanding the role of sea ice in the climate system. They are also a prerequisite for meaningful prediction. To improve the simulated sea ice properties, we develop an objective parameter optimization system for a coupled sea ice–ocean model based on a genetic a...

Assimilation of remote-sensing products of sea ice thickness (SIT) into sea ice–ocean models has been shown to improve the quality of sea ice forecasts. Key open questions are whether assimilation of lower-level data products such as radar freeboard (RFB) can further improve model performance and what performance gains can be achieved through joint...

The first full transarctic section of ²²⁸Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the transpolar drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased ²²⁸Ra input is attributed to stronger wave action on sh...

The extended multiple linear regression technique is used to determine changes in anthropogenic carbon in the intermediate layers of the Eurasian Basin based on occupations from four cruises between 1996 and 2015. The results show a significant increase in basin-wide anthropogenic carbon storage in the Nansen Basin (0.44–0.73 ± 0.14 mol C·m⁻²·year⁻...

Any use of observational data for data assimilation requires adequate information of their representativeness in space and time. This is particularly important for sparse, non-synoptic data, which comprise the bulk of oceanic in situ observations in the Arctic. To quantify spatial and temporal scales of temperature and salinity variations, we estim...

Assimilation of remote sensing products of sea ice thickness (SIT) into sea ice-ocean models has been shown to improve the quality of sea ice forecasts. Open questions are whether the assimilation of rawer products such as radar freeboard (RFB) can achieve yet a better performance and what performance gain can be achieved by the joint assimilation...

The ability to forecast sea ice (both extent and thickness) and weather conditions are the major factors when it comes to safe marine transportation in the Arctic Ocean. This paper presents findings focusing on sea ice and weather prediction in the Arctic Ocean for navigation purposes, in particular along the Northeast Passage. Based on comparison...

This introduction to the special issue presents an overview of the wide range of results produced during the European Union project Arctic Climate Change, Economy and Society (ACCESS). This project assessed the main impacts of climate change on Arctic Ocean’s geophysical variables and how these impending changes could be expected to impact directly...

Any use of observational data for data assimilation requires adequate information of their representativeness in space and time. This is particularly important for sparse, non-synoptic data, which comprise the bulk of oceanic in-situ observations in the Arctic. To quantify spatial and temporal scales of temperature and salinity variations, we estim...

Of the wide variety of dumped objects containing radioactive materials in the Arctic seas, the submarine K-27 constitutes a major risk due to the large amount of highly enriched uranium onboard and its location in shallow waters. As the matter of potential operations involving raising of the submarine have entered the public arena, a priori assessm...

There is increasing concern regarding the issue of dumped nuclear waste in the Arctic Seas and in particular dumped objects with Spent Nuclear Fuel (SNF). Amongst dumped objects in the Arctic, the dumped Russian submarine K-27 has received great attention as it contains two reactors with highly enriched fuel and lies at a depth of about 30 m under...

The Columbia Climate Center, in partnership with World Wildlife Fund, Woods Hole Research Center, and Arctic 21, held a workshop titled A 5 C Arctic in a 2 C World on July 20 and 21, 2016. The workshop was co-sponsored by the International Arctic Research Center (University of Alaska Fairbanks), the Arctic Institute of North America (Canada), the M...

The transport of nuclear or radioactive materials and the presence of nuclear powered vessels pose risks to the Northern Seas in terms of potential impacts to man and environment as well socio-economic impacts. Management of incidents involving actual or potential releases to the marine environment are potentially difficult due to the complexity of...

The recent thinning and shrinking of the Arctic sea ice cover has increased the interest in seasonal sea ice forecasts. Typical tools for such forecasts are numerical models of the coupled ocean sea ice system such as the North Atlantic/Arctic Ocean Sea Ice Model (NAOSIM). The model uses as input the initial state of the system and the atmospheric...

Empirical error functions for 6 different low-resolution Arctic sea-ice drift products are presented on monthly time-scales. To assess the error statistics of the Eulerian ice-drift products, we use high-resolution Lagrangian sea-ice drift obtained from synthetic aperture radar (SAR) images. We processed the Lagrangian drift to Eulerian drift vecto...

Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings heat, fresh water and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper pathways of PW are investigated using simulations with six state-of-the art regional a...

We present a quantitative network design (QND) study of the Arctic sea ice–ocean system using a software tool that can evaluate hypothetical observational networks in a variational data assimilation system. For a demonstration, we evaluate two idealised flight transects derived from NASA's Operation IceBridge airborne ice surveys in terms of their...

Siberian river water is a first-order contribution to the Arctic freshwater budget, with the Ob, Yenisey, and Lena supplying nearly half of the total surface freshwater flux. However, few details are known regarding where, when and how the freshwater transverses the vast Siberian shelf seas. This paper investigates the mechanism, variability and pa...

Time-space varying uncertainty maps of monthly mean Arctic summer ice drift are presented. To assess the error statistics of two low-resolution Eulerian ice drift products, we use high-resolution Lagrangian ice motion derived from synthetic aperture radar (SAR) imagery. The Lagrangian trajectories from the SAR data are converted to an Eulerian form...

International Workshop on Polar-lower Latitude Linkages in Weather and Climate Prediction What: Eighty experts from twenty different countries met to assess recent progress in, and new directions for, our understanding of the mechanisms governing polar-lower latitude linkages and their role in weather and climate prediction including services. Wh...

We present a quantitative network design (QND) study of the Arctic sea ice-ocean system using a software tool that can evaluate hypothetical observational networks in a variational data assimilation system. For a demonstration, we evaluate two idealised flight transects derived from NASA's Operation IceBridge airborne ice surveys in terms of their...

Large freshwater anomalies clearly exist in the Arctic Ocean. For example, liquid freshwater has accumulated in the Beaufort Gyre in the decade of the 2000s compared to 1980-2000, with an extra ≈ 5000 km3 — about 25% — being stored. The sources of freshwater to the Arctic from precipitation and runoff have increased between these periods (most of t...

With a numerical model we test the sensitivity of the Arctic Ocean circulation at mid-depth (212-1200 m) to the change in the sea ice rheology parameter P* that controls the sea ice compressive strength. We show that the reduction of the sea ice strength via P* within commonly used envelope reduces the sea ice extent and consequently enhances the o...

An intercomparison of four low-resolution remotely sensed ice-drift products in the Arctic Ocean is presented. The purpose of the study is to examine the uncertainty in space and time of these different drift products. The comparison is based on monthly mean ice drifts from October 2002 to December 2006. The ice drifts were also compared with avail...

The upper Arctic Ocean has experienced significant freshening from the 1990s to late 2000s. A very strong Beaufort Gyre and a temporarily freshened Transpolar Drift raise the question how much longer the Arctic Ocean can accumulate freshwater. Since 2006, autonomous CTD profilers have allowed to estimate upper ocean properties in the Arctic through...

Freshwater in the Arctic Ocean plays an important role in the regional ocean circulation, sea ice, and global climate. From salinity observed by a variety of platforms, we are able, for the first time, to estimate a statistically reliable liquid freshwater trend from monthly gridded fields over all upper Arctic Ocean basins. From 1992 to 2012 this...

Atlantic water is entering the Arctic ocean through the Fram Strait and through the Barents Sea. The Barents Sea branch is larger in volume but it transports only a low amount of heat. The Fram Strait branch is comparatively smaller in volume but warmer. We have performed an ensemble of model experiments with different sea ice parameters and discov...

We applied genetic algorithms to a parameter optimization problem in a coupled ocean - sea ice model, and examined applicability and efficiency of this approach from the point of view of a practical use for sea ice - ocean simulation in the Arctic Ocean. Several series of parameter optimization experiments were performed by minimizing a cost functi...

Two types of optimization methods were applied to a parameter optimization problem in a coupled ocean-sea ice model, and applicability and efficiency of the respective methods were examined. One is a finite difference method based on a traditional gradient descent approach, while the other adopts genetic algorithms as an example of stochastic appro...

1] The Arctic freshwater (FW) has been the focus of many modeling studies, due to the potential impact of Arctic FW on the deep water formation in the North Atlantic. A comparison of the hindcasts from ten ocean-sea ice models shows that the simulation of the Arctic FW budget is quite different in the investigated models. While they agree on the ge...

Anthropogenic radionuclides released into European coastal waters from nuclear fuel reprocessing plants at Sellafield (UK) and La Hague (France) flow northward through the Nordic Seas and label Atlantic Water (AW) entering the Arctic Ocean. Transport of the soluble radionuclide 129I through the Arctic Ocean has been simulated using a numerical mode...

The current and future distribution of sea-ice in the Arctic is of interest to various scientific and non-scientific groups e.g. policymakers, fisheries and shipping companies. Their focus is on the development during the next decades. The assessment of Arctic sea-ice is challenging due to internal variability being superimposed on the general tren...

Observational based assessment of the fresh water content

Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, and also a researcher at Ocean Atmosphere Systems, Hamburg, Germany. Abst ract. In recent decades, the Arctic Ocean has changed dramatically. Exchanges through the main oceanic gateways indicate two main processes of global climatic importance-poleward oceanic heat flux i...

Two anomalously warm inflow pulses into the Atlantic Water Layer of the Arctic Ocean have occurred since the late 1980s. As a consequence temperatures of the Arctic basins at 200–800 m depth have increased considerably in comparison to earlier decades. The warm inflow pulses also had a low density. Owing to the decadal time scale of the circulation...

Unprecedented summer-season sampling of the Arctic Ocean during the period 2006–2008 makes possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins. In comparison to observations from 1992 to 1999, LFW content relative to a salinity of 35 in the layer from the surface to the 34 isohaline increased by 8400...

99Tc levels were measured in seawater samples collected between 2000 and 2002 in the West Spitsbergen Current (WSC) and along the western coast of Svalbard or Spitzbergen and compared with available oceanographic 3-D modelling results for the late 1990s. Additional data from related regions are also presented in order to support the data interpreta...

Current predictions as to the impacts of climate change in general and Arctic climate change in particular are such that a wide range of processes relevant to Arctic contaminants are potentially vulnerable. Of these, radioactive contaminants and the processes that govern their transport and fate may be particularly susceptible to the effects of a c...

Over a decade of mooring measurements in the western Fram Strait at 78°50′N shows that the annual mean liquid freshwater flux (FWF) in the East Greenland Current is relatively constant at −1274 ± 453 km3 yr−1 (−40.4 ± 14.4 mSv) despite the fact that the annual mean total volume transport of the EGC has more than doubled since 2001. This...

Compartment models are widely used for the evaluation of radiological consequences to man and biota in the marine environment over large spatial and long temporal scales. The model developed at the Norwegian Radiation Protection Authority (NRPA) is based on a compartment modelling approach that includes terms describing dispersion of radionuclides...

We present the late summer distribution and transports of freshwater components in the upper western part of the Fram Strait during 1998, 2004 and 2005. Hydrographic data and and water δ18O values are analyzed to distinguish Atlantic Water, ice-melt (IMW) and freshwater removal from ice formation (IFW), and Meteoric Water (precipitation and riverin...

We present the late summer distribution and transports of freshwater components in the upper western part of the Fram Strait during 1998, 2004 and 2005. Hydrographic data and and water δ¹⁸O values are analyzed to distinguish Atlantic Water, ice-melt (IMW) and freshwater removal from ice formation (IFW), and Meteoric Water (precipitation...

The past two decades saw a steady decrease of summer Arctic sea ice extent. The 2007 value was yet considerably lower than expected from extrapolating the long-term trend. We present a quantitative analysis of this extraordinary event based on the adjoint of a coupled ocean-sea ice model. This new approach allows to efficiently assess the sensitivi...

1] The ability to simulate the past variability of the sea ice-ocean system is of fundamental interest for the identification of key processes and the evaluation of scenarios of future developments. To achieve this goal atmospheric surface fields are reconstructed by statistical means for the period 1900 to 1997 and applied to a coupled sea ice-oce...

The inflow of water from the Atlantic Ocean has long been known to be an essential source of heat and salt for the Nordic Seas and the Arctic Ocean (Hansen and Østerhus 2000). However, only in the period of the projects VEINS (Variability of Exchanges in the Northern Seas) and ASOF (Arctic /Subarctic Ocean Flux Study) a coordinated effort to quanti...

The fresh water export from the Arctic has not been measured yet. The major problem lies in the transport over the shallow East Greenland shelf that is not easily accessible for oceanographic vessels and so far has been off-limits for moored instrumentation. Even if we would be able to start measurements now, we would have no statistics to evaluate...

Abstract Upper ocean,conditions in the Greenland Sea are investigated for detecting preconditioning of the water column,for deep convection and how,these conditions are simulated,in the models. Observations indicate that periods of intense deep-water formation were also associated with dense upper ocean water masses, hence we focus on the upper oce...

1] Observations indicate that the occurrence of dense upper-ocean water masses coincides with periods of intense deep-water formation in the Greenland Sea. This paper focuses on the upper-ocean hydrography of the area and its simulation in models. We analyze properties that reside below the summer mixed layer at 200 m and carry the winter mixing si...

A series of sensitivity experiments using a coupled regional atmosphere-ocean-ice model of the Arctic has been conducted in order to identify the requirements needed to reproduce observed sea-ice conditions and to address uncertainties in the description of Arctic processes. The ability of the coupled model to reproduce observed summer ice retreat...

We use a subset of models from the coordinated experiment of the Arctic Ocean Model Intercomparison Project (AOMIP) to analyze differences in intensity and sense of rotation of Atlantic Water circulation. We focus on the interpretation of the potential vorticity (PV) balance. Results differ drastically for the Eurasian and the Amerasian Basins of t...

As a part of the Arctic Ocean Model Intercomparison Project, results from 10 Arctic ocean/ice models are intercompared over the period 1970 through 1999. Models' monthly mean outputs are laterally integrated over two subdomains (Amerasian and Eurasian basins), then examined as functions of depth and time. Differences in such fields as averaged temp...

Monthly energetics of the Arctic Ocean are estimated based on results from six different coupled ice-ocean models. The components of the kinetic, potential and available potential energies, energy conversion and forcing rates are studied. The energy balances derived from the models differ significantly in the abyss, notably regarding the conversion...

This State of the Arctic Report presents a review of recent data by an international group of scientists who developed a consensus on the information content and reliability. The report highlights data primarily from 2000 to 2005 with a first look at winter 2006, providing an update to some of the records of physical processes discussed in the Arct...

As the world warms, the expectation is that the freshwater outflows from the Arctic Ocean to the North Atlantic will strengthen and may act to suppress the rate of the climatically-important Atlantic meridional overturning circulation. Hitherto, however, we have lacked the system of measurements required to estimate the totality of the freshwater f...

This State of the Arctic Report presents a review of recent data by an international group of scientists who developed a consensus on the information content and reliability. The report highlights data primarily from 2000 to 2005 with a first look at winter 2006, providing an update to some of the records of physical processes discussed in the Arct...

The impact of North Atlantic Current (NAC) volume, heat, and salt transport variability onto the Nordic Seas and the Arctic Ocean is investigated using numerical hindcast and sensitivity experiments. The ocean-sea ice model reproduces observed propagation pathways and speeds of SST anomalies. Signals reaching the entrance to the Nordic Seas between...

1] A large pool of freshwater formed of ice and runoff is hosted by the Arctic Ocean. It exits through the Canadian Archipelago and Fram Strait to enter the North Atlantic deep water production regions. Using a numerical model and observations we trace a strong freshwater release to subpolar waters in the mid-1990s. In contrast to the ice export dr...

Model development and simulations represent a comprehensive synthesis of observations with advances in numerous disciplines (physics; mathematics; and atmospheric, oceanic, cryospheric, and related sciences), enabling hypothesis testing via numerical experiments. For the Arctic Ocean, modeling has become one of the major instruments for understandi...

This study was motivated by a strong warming signal seen in mooring-based and oceanographic survey data collected in 2004 in the Eurasian% Basin of the Arctic Ocean. The source of this and earlier Arctic Ocean changes lies in interactions between polar and sub-polar basins. Evidence suggests such changes are abrupt, or pulse-like, taking the form o...

Oxygen and stable carbon isotope records along the growth direction on shells of the bivalve species Astarte borealis and Serripes groenlandicus reliably record all important aspects of the bottom water hydrography in the shallow southeastern Kara Sea, despite uncertainties about the isotopic range due to sparse sampling and the possibility of grow...

1] A regional coupled ice-ocean model for the Kara Sea, forced with boundary conditions from a large-scale North Atlantic/Arctic Ocean Model, is used to study dispersion and export of freshwater from Ob and Yenisei rivers toward the Arctic Ocean and the Laptev Sea, for the period 1996–2001. The years 1998 and 1999 were characterized by a strong pos...

Monitoring of the marine environment for radioactivity, for both radiological protection and oceanographic purposes, remains an expensive and labour intensive activity due to the large sample volumes needed and the complex and lengthy analytical procedures required to measure low levels of contamination. Because of this, some consideration must be...