Arctic Climate

Critique of the tracer-tracer correlation technique and its potential to analyze polar ozone loss in chemistry-climate models

by Carsten Lemmen

Co-authored with Rolf Müller, Paul Konopka, and Martin Dameris

The tracer-tracer correlation technique (TRAC) has been widely employed to infer chemical ozone loss from... more The tracer-tracer correlation technique (TRAC) has been widely employed to infer chemical ozone loss from observations. Yet, its applicability to chemistry-climate model(CCM) data is disputed. Here, we report the successful application of TRAC on theresults of a CCM simulation. By comparing TRAC-calculated ozone loss to ozone lossderived with the passive ozone method in a chemistry transport model we differentiateeffects of internal mixing and cross vortex boundary mixing on a TRAC referencecorrelation. As a test case, we consider results of a cold Arctic winter/spring episode froman E39/C experiment, where typical features, for example, sufficient polar stratosphericcloud formation potential, denitrification and dehydration, and intermittent and finalstratospheric warming events, are simulated. We find that internal mixing does not impact the TRAC-derived reference correlation at all. Mixing across the vortex boundary wouldlead to an underestimation of ozone loss by 10% when calculated with TRAC. We provide arguments that TRAC is a consistent and conservative method to derive chemicalozone loss and can be used to extract its chemical signature also from CCM simulations. As a consequence, we will be able to provide a lower bound for chemical ozone loss for model simulations where a passive ozone tracer is not available

Smoluchowski coagulation models of sea ice thickness distribution dynamics

by Daniel Godlovitch

Observations of sea ice thickness distributions typically display an exponential decrease (or ‘tail’) in the frequency... more Observations of sea ice thickness distributions typically display an exponential decrease (or ‘tail’) in the frequency of ice above the limit of thermodynamic growth. Any sea ice which is more than approximately 2m thick is formed by redistribution processes involving the damaging and ridging of ice, and modelling the dynamic evolution of the thickness distribution of sea ice requires that these processes be adequately represented. In this work, an idealised zero-dimensional model of the redistribution process and the evolution of the thickness distribution is presented, with the aim of determining the processes responsible for the ubiquity of the exponential tail of the distribution. The model is stochastic in nature, and redistribution events occur with probabilities which are dependent on their energetic magnitudes. Unlike many existing models, no detailed ice rheology is included. The model is able to produce qualitatively realistic thickness distributions and thickness distribution dynamics. Sensitivity analysis of the model demonstrates a robust response to the exact form of the energetic dependence of redistribution. However, the qualitative features of the simulated populations are strongly affected by the description of the manner in which redistribution events transfer ice between thickness categories. The construction and behaviour of the sea ice model is compared to a family of equations known as Smoluchowski Coagulation Models which feature similar dynamics and are known to produce exponentially-distributed populations. We conclude that the exponential tail of the thickness distribution arises due to the nature of the redistribution process, rather than because of any detailed features of rheological properties of the ice, or any spatial aspect of the redistribution process.

The creation of Ruskaya Arktika: environmental project hiding Arctic strategy in Russia

by Camille Hamm

Co-authored with Sébastien Maffione (Arctic Studies March 2011).

Modeling density dependence and climatic disturbances in caribou: a case study from the Bathurst Island complex, Canadian High Arctic

by Mike Ferguson

Tews J, Ferguson MAD, Fahrig L. 2007. Modeling density dependence and climatic disturbances in caribou: A case study from the Bathurst Island complex, Canadian high arctic. Journal of Zoology 272(2): 209-217.

Keywords: climate change; density independence; environmental stochasticity; Peary caribou; population dynamics; population viability analysis; simulation model

Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the... more Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the Canadian High Arctic. Because of severe population declines following years of unfavorable winter weather with ice coating on the ground or thicker snow cover, it is believed that density-independent disturbance events are the primary driver for Peary caribou population dynamics. However, it is unclear to what extent density dependence may affect population dynamics of this species. Here, we test for different levels of density dependence in a stochastic, single-stage population model, based on available empirical information for the Bathurst Island complex (BIC) population in the Canadian High Arctic. We compare predicted densities with observed densities during 1961–2001 under various assumptions of the strength of density dependence. On the basis of our model, we found that scenarios with no or very low density dependence led to population densities far above observed densities. For average observed disturbance regimes, a carrying capacity of 0.1 caribou km−2 generated an average caribou density similar to that estimated for the BIC population over the past four decades. With our model we also tested the potential effects of climate change-related increases in the probability and severity of disturbance years, that is unusually poor winter conditions. On the basis of our simulation results, we found that, in particular, potential increases in disturbance severity (as opposed to disturbance frequency) may pose a considerable threat to the persistence of this species.

Status of Peary caribou and muskox populations on Bathurst Island, NWT, August 1981

by Mike Ferguson

Ferguson. 1987. Status of Peary Caribou and Muskox Populations on Bathurst Island, N. W.T., August 1981. Arctic 40: 131-137.

Key words: Northwest Territories, Peary caribou, muskoxen, population status, distribution, management

An aerial survey of Bathurst Island, Northwest Territories, Canada, was conducted 10-13 August 1981 to determine if... more An aerial survey of Bathurst Island, Northwest Territories, Canada, was conducted 10-13 August 1981 to determine if Peary caribou (Rangifer tarandus pearyi) and muskoxen (Ovibos moscharus) had recovered since die-offs in the early 1970s. Sampling intensity was 26%, except for 74% over Polar Bear Pass on central Bathurst Island. Populations of 289 Peary caribou and 208 muskoxen were estimated. The proportion of calves among classified animals was 19% for caribou and 16% for muskoxen. Caribou were concentrated on northern Bathurst, preferring elevations 151-300 m above sea level (asl). Muskoxen were concentrated in southern and central Bathurst Island, preferring elevations below 150 m asl. Spatial separation of the two species during the survey suggested little or no range overlap during late summer. Calf production and/or summer survival in 1981 was significantly greater than in 1974. The 1981 caribou and muskox estimates were only slightly greater than in August 1974. Thus the populations estimated in 1981 showed no marked overall recovery since 1974. Prohibition of harvesting of both species should continue on Bathurst Island. An “extensive-then-intensive” survey design is recommended for future work, based on statistical problems associated with the 1981 and previous surveys

Arctic tundra caribou and climatic change: Questions of temporal and spatial scales

by Mike Ferguson

Ferguson, M.A.D. 1996. Arctic tundra caribou and climatic change: Questions of temporal and spatial scales. Geoscience Canada 23: 245-252.

Climatic changes have affected populations of caribou and reindeer (Rangifer tarandus) at scales ranging from a single... more Climatic changes have affected populations of caribou and reindeer (Rangifer tarandus) at scales ranging from a single winter to tens of thousands of years, and from micro-habitats to entire continents. Individuals, populations and the species have adapted to these climatic changes, however, producing complex evolutionary and ecological issues requiring multi-scale, interdisciplinary research. Caribou populations wintering on arctic tundra may be most susceptible to the impacts of anthropogenic climatic change, given the low productivity of their forage, the severity and duration of the winters, and the physical barriers that limit dispersal.

Sub-speciation of Rangifer tarandus hypotheticaly occurred during the Wisconsin glaciation. Recent genetic analyses support the current classification of subspecies, except that Baffin Island caribou may be distinct from barren-ground caribou, R. t. groenlandicus, on mainland Northwest Territories. Baffin caribou may have originated from a small ancestral population in a refugium on Baffin Island during the Wisconsin glaciation; or, they may have originated from immigrants after the Wisconsin glaciation, later experiencing a severe population bottleneck.

On a shorter time scale, recent research has suggested that density-independent climatic events occurring over a single winter have caused at least one major population decline among Peary caribou on the Queen Elizabeth Islands. Dramatic fluctuations of Greenland populations over the past 200 years have been attributed to climatic changes. However, the onset of some population changes on western Greenland have been inconsistent with the timing of climatic changes. Inuit knowledge of Baffin caribou and studies of tundra caribou on Svalbard, Coats and Southampton islands, South Georgia, and Norway suggest that caribou populations are affected primarily by density-dependent grazing impacts on forage that can last several decades. The discrepancy between these views may be caused by differences in the temporal and spatial scales over which scientific investigations have been conducted, and the measurement of only some ecological factors. Arctic ecological studies require extensive spatial and temporal data before impacts of anthropogenic climate change can be assessed. This will require a long-term interdisciplinary study integrating scientific data from several disciplines, as well as Inuit knowledge.

Arctic inversion strength in climate models

by Brian Medeiros

Medeiros, B., C. Deser, R. A. Tomas, J. E. Kay, 2011: Arctic inversion strength in climate models. Journal of Climate, 24(17), pp. 4733-4740 doi: 10.1175/2011JCLI3968.1

Recent work indicates that climate models have a positive bias in the strength of the winter- time low-level... more Recent work indicates that climate models have a positive bias in the strength of the winter- time low-level temperature inversion over the high-latitude northern hemisphere. It has been argued this bias leads to underestimates of the Arctic’s surface temperature response to an- thropogenic forcing. Here the bias in inversion strength is revisited. The spatial distribution of low-level stability is found to be bimodal in climate models and observational reanalysis products, with low-level inversions represented by a stable primary mode over the interior Arctic Ocean and adjacent continents, and a secondary unstable mode over the Atlantic Ocean. Averaging over these differing conditions is detrimental to understanding the origins of the inversion strength bias. While nearly all of the 21 models examined overestimate the area-average inversion strength, conditionally sampling the two modes shows about half the models are biased because of the relative partitioning of the modes and half because of biases within the stable mode.

A Characterization of the Present-Day Arctic Atmosphere in CCSM4

by Brian Medeiros

de Boer, G., W. Chapman, J. E. Kay, B. Medeiros, M. D. Shupe, S. Vavrus, J. Walsh, In Press J. Climate (CCSM4 Special Collection)
doi: http://dx.doi.org/10.1175/JCLI-D-11-00228.1

Simulation of key features of the Arctic atmosphere in the fourth version of the Community Climate System Model... more Simulation of key features of the Arctic atmosphere in the fourth version of the Community Climate System Model (CCSM4) is evaluated against observational and reanalysis datasets for the present-day (1981-2005). Surface air temperature, sea level pressure, cloud cover and phase, precipitation and evaporation, the atmospheric energy budget and lower tropospheric stability are evaluated. Simulated surface air temperatures are found to be slightly too cold when compared with ERA-40. Spatial patterns and temporal variability are well simulated. Evaluation of the sea level pressure demonstrates some large biases, most noticeably an under-simulation of the Beaufort High during spring and autumn. Monthly Arctic-wide biases of up to 13 mb are reported. Cloud cover is under-predicted for all but summer months, and cloud phase is demonstrated to be different from observations. Despite low cloud cover, simulated all-sky liquid water paths are too high, while ice water path was generally too low. Precipitation is found to be excessive over much of the Arctic compared to ERA-40 and GPCP estimates. With some exceptions, evaporation is well captured by CCSM4, resulting in P-E estimates that are too high. CCSM4 energy budget terms show promising agreement with estimates from several sources. The most noticeable exception to this are TOA fluxes that are found to be too low while surface fluxes are found to be too high during summer months. Finally, the lower troposphere is found to be too stable when compared to ERA-40 during all times of year, but particularly during spring and summer months.

An Early Albian Arctic-type ammonite Arcthoplites from Hokkaido, northern Japan, and its paleobiogeographic and paleoclimatological implications

by Yasuhiro Iba

Iba, 2009 An Early Albian Arctic-type ammonite Arcthoplites from Hokkaido, northern Japan, and its paleogeographic and paleoclimatological implications. Journal of Asian Earth Science, 34, 46-50

An Early Albian Arctic-type ammonite Arcthoplites was discovered from the Kamiji Formation of the Yezo Group in the... more An Early Albian Arctic-type ammonite Arcthoplites was discovered from the Kamiji Formation of the Yezo Group in the Nakagawa area, northern Hokkaido, northern Japan. This is the first reliable record of a hoplitid ammonite from Japan and clearly indicates the distribution of an Arctic fauna in the middle lat- itudes of the North Pacific at that time. Synchronously with the appearance of this Arctic-type ammonite, the tropical Tethyan biota (Mesogean taxa) disappeared from Hokkaido and elsewhere in the Northwest Pacific. These biogeographic changes suggest the existence of a ‘‘cooling” episode in the Early Albian North Pacific.

EU Arctic Footprint and Policy Assessment

by Christine Polzin

Final report co-authored with S. Cavalieri, E. McGlynn, S. Stoessel, F. Stuke, M. Bruckner, T. Koivurova, N. Sellheim, A. Stepien, K. Hossain, S. Duyck, and A.E. Nilsson

The EU Arctic Footprint and Policy Assessment report assesses the EU‘s current footprint on the Arctic environment and... more The EU Arctic Footprint and Policy Assessment report assesses the EU‘s current footprint on the Arctic environment and evaluates how it could change over time. The effectiveness of the EU‘s current environment-related policies is analysed, including how these policies relate to current and future footprint scenarios. Options for improving EU policy are presented.