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  • 1
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    Multi-century changes in ocean and land contributions to climate-carbon feedbacks (2015)
    Wiley
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    Publication Date: 2015-04-22
    Description: Improved constraints on carbon cycle responses to climate change are needed to inform mitigation policy, yet our understanding of how these responses may evolve after 2100 remains highly uncertain. Using the Community Earth System Model (v1.0), we quantified climate-carbon feedbacks from 1850 to 2300 for the Representative Concentration Pathway 8.5 and its extension. In three simulations, land and ocean biogeochemical processes experienced the same trajectory of increasing atmospheric CO 2 . Each simulation had a different degree of radiative coupling for CO 2 and other greenhouse gases and aerosols, enabling diagnosis of feedbacks. In a fully coupled simulation, global mean surface air temperature increased by 9.3 K from 1850 to 2300, with 4.4 K of this warming occurring after 2100. Excluding CO 2 , warming from other greenhouse gases and aerosols was 1.6 K by 2300, near a 2 K target needed to avoid dangerous anthropogenic interference with the climate system. Ocean contributions to the climate-carbon feedback increased considerably over time, and exceeded contributions from land after 2100. The sensitivity of ocean carbon to climate change was found to be proportional to changes in ocean heat content, as a consequence of this heat modifying transport pathways for anthropogenic CO 2 inflow and solubility of dissolved inorganic carbon. By 2300 climate change reduced cumulative ocean uptake by 330 Pg C, from 1410 Pg C to 1080 Pg C. Land fluxes similarly diverged over time, with climate change reducing stocks by 232 Pg C. Regional influence of climate change on carbon stocks was largest in the North Atlantic Ocean and tropical forests of South America. Our analysis suggests that after 2100, oceans may become as important as terrestrial ecosystems in regulating the magnitude of climate-carbon feedbacks.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Paleodust variability since the Last Glacial Maximum and implications for iron inputs to the ocean (2016)
    Wiley
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    Publication Date: 2016-04-01
    Description: Changing climate conditions affect dust emissions and the global dust cycle, which in turn affects climate and biogeochemistry. In this study we use observationally-constrained model reconstructions of the global dust cycle since the Last Glacial Maximum, combined with different simplified assumptions of atmospheric and sea ice processing of dust-borne iron, to provide estimates of soluble iron deposition to the oceans. For different climate conditions, we discuss uncertainties in model-based estimates of atmospheric processing and dust deposition to key oceanic regions, highlighting the large degree of uncertainty of this important variable for ocean biogeochemistry and the global carbon cycle. We also show the role of sea ice acting as a time buffer and processing agent, which results in a delayed and pulse-like soluble iron release into the ocean during the melting season, with monthly peaks up to ~17 Gg/month released into the Southern Oceans during the LGM.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Arctic System Reanalysis improvements in topographically-forced winds near Greenland (2016)
    Wiley
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    Publication Date: 2016-03-25
    Description: Southern Greenland is home to a number of weather systems characterized by high speed low-level winds that are the result of topographic flow distortion. These systems include tip jets, barrier winds and katabatic flows. Global atmospheric reanalyses have proven to be important tools in furthering our understanding of these systems and their role in the climate system. However, there is evidence that their mesoscale structure may be poorly resolved in these global products. Here output from the regional Arctic System Reanalysis (ASRv1–30 km and ASRv2–15 km grid resolutions) are compared to the global ERA-Interim Reanalysis (ERA-I–80 km grid resolution), focusing on their ability to represent winds in the vicinity of southern Greenland. Comparisons are made to observations from surface and upper-air stations, as well as from research aircraft flights during the Greenland Flow Distortion Experiment (GFDex). The ERA-I reanalysis has a tendency to underestimate high wind speeds and overestimate low wind speeds, which is reduced in ASRv1 and nearly eliminated in ASRv2. In addition, there is generally a systematic reduction in the root mean square error between the observed and the reanalysis wind speeds from ERA-I to ASRv1 to ASRv2, the exception being low-level marine winds where the correspondence is similar in all reanalyses. Case studies reveal that mesoscale spatial features of the wind field are better captured in ASRv2 as compared to the ERA-I or ASRv1. These results confirm that a horizontal grid size on the order of 15 km is needed to characterize the impact that Greenland's topography has on the regional wind field and climate. However even at this resolution, there are still features of the wind field that are under-resolved.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 4
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    Shelfbreak Downwelling in the Alaskan Beaufort Sea (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The oceanographic response and atmospheric forcing associated with downwelling along the Alaskan Beaufort Sea shelf/slope is described using mooring data collected from August 2002 to September 2004, along with meteorological time series, satellite data, and reanalysis fields. In total, 55 downwelling events are identified with peak occurrence in July and August. Downwelling is initiated by cyclonic low‐pressure systems displacing the Beaufort High and driving westerly winds over the region. The shelfbreak jet responds by accelerating to the east, followed by a depression of isopycnals along the outer shelf and slope. The storms last 3.25 ± 1.80 days, at which point conditions relax toward their mean state. To determine the effect of sea ice on the oceanographic response, the storms are classified into four ice seasons: open water, partial ice, full ice, and fast ice (immobile). For a given wind strength, the largest response occurs during partial ice cover, while the most subdued response occurs in the fast ice season. Over the 2‐year study period, the winds were strongest during the open water season; thus, the shelfbreak jet intensified the most during this period and the cross‐stream Ekman flow was largest. During downwelling, the cold water fluxed off the shelf ventilates the upper halocline of the Canada Basin. The storms approach the Beaufort Sea along three distinct pathways: a northerly route from the high Arctic, a westerly route from northern Siberia, and a southerly route from south of Bering Strait. Differences in the vertical structure of the storms are presented as well.
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Storm-induced upwelling of high pCO2 waters onto the continental shelf of the western Arctic Ocean and implications for carbonate mineral saturation states (2012)
    Wiley
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    Publication Date: 2012-04-11
    Description: The carbon system of the western Arctic Ocean is undergoing a rapid transition as sea ice extent and thickness decline. These processes are dynamically forcing the region, with unknown consequences for CO2 fluxes and carbonate mineral saturation states, particularly in the coastal regions where sensitive ecosystems are already under threat from multiple stressors. In October 2011, persistent wind-driven upwelling occurred in open water along the continental shelf of the Beaufort Sea in the western Arctic Ocean. During this time, cold ( 32.4) halocline water—supersaturated with respect to atmospheric CO2 (pCO2 〉 550 μatm) and undersaturated in aragonite (Ωaragonite 〈 1.0) was transported onto the Beaufort shelf. A single 10-day event led to the outgassing of 0.18–0.54 Tg-C and caused aragonite undersaturations throughout the water column over the shelf. If we assume a conservative estimate of four such upwelling events each year, then the annual flux to the atmosphere would be 0.72–2.16 Tg-C, which is approximately the total annual sink of CO2 in the Beaufort Sea from primary production. Although a natural process, these upwelling events have likely been exacerbated in recent years by declining sea ice cover and changing atmospheric conditions in the region, and could have significant impacts on regional carbon budgets. As sea ice retreat continues and storms increase in frequency and intensity, further outgassing events and the expansion of waters that are undersaturated in carbonate minerals over the shelf are probable.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Northern Bering Sea tip jets (2012)
    Wiley
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    Publication Date: 2012-04-28
    Description: Low-level regions of high wind speed known as tip jets have been identified near Cape Farewell, Greenland's southernmost point. These wind systems contribute to this area being the windiest location on the ocean's surface and play an important role in the regional weather and climate. Here we present the first analysis of the wind systems that make the Siberian coast of the northern Bering Sea the windiest location in the North Pacific Ocean during the boreal winter. In particular we show that tips jets characterized by enhanced northeasterly winds occur in the vicinity of the two prominent headlands along the coast, Cape Navarin and Cape Olyutorsky. The advance of sea ice in the region is shown to impact the frequency and location of the high speed winds in the vicinity of these two capes. Furthermore, we show that these jets are associated with the interaction of extra-tropical cyclones with the high topography of the Koryak Mountain range, situated just inland of the capes. The windstress imparted to the ocean via the tip jets is argued to help drive the formation of dense water in winter in the northern Bering Sea, thus playing an important role in the regional oceanic circulation.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Surface pressure record of Tibetan Plateau warming since the 1870s (2012)
    Wiley
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    Publication Date: 2012-05-12
    Description: The Tibetan Plateau (TP) is the world's highest and largest plateau. By acting as an elevated thermal source as well as a topographic barrier, the TP has a profound impact on both local weather and global climate. The TP has recently been warming at a faster rate than the entire Northern Hemisphere. However, the lack of instrumental records prior to the 1950s limits our ability to place this recent warming in a longer-term context. Here we show that over the plateau, because of its high elevation, the surface pressure is a proxy for surface air temperature and that since the 1870s there has been a statistically significant increase in surface pressure over the TP, that has undergone an acceleration since the 1980s. There is also a compensatory decrease in surface pressure in the surrounding lower elevation region. Furthermore, we show that since the 1870s the surface pressure over the plateau is correlated with the Northern Hemisphere temperature record at a statistical significance that exceeds the 99 percentile. Finally, the trend in surface pressure over the plateau is consistent with an increase in annual mean surface air temperature of ∼0.4°C since the 1870s and an increase of ∼1°C since the 1980s. The long-term warming over the TP derived from the surface pressure trend is of the same order as the long-term hemispheric warming. This suggests that the increased rate of warming recently observed over the plateau is not a long-term phenomenon. Copyright © 2012 Royal Meteorological Society
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 8
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    Decadal variability and a recent amplification of the summer Beaufort Sea High (2012)
    Wiley
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    Publication Date: 2012-05-19
    Description: The Beaufort Sea High (BSH), an anti-cyclone over the Beaufort Sea, is an important feature of the summer atmospheric circulation over the Arctic Ocean. For example, years characterized by low Arctic sea ice extent are typically associated with the presence of a stronger BSH; with the opposite occurring during years with high sea ice extent. In this paper, we show that there exists variability on the decadal time scale in the intensity and location of the summer BSH. We also show that there has been a trend towards a stronger summer BSH that began in the late 1990s. This trend is shown to be coincident with a tendency towards a reduction in cyclogenesis during the summer over the Beaufort Sea. We argue that that these trends are the result of a warming of the troposphere in the western Arctic and the concomitant reduction in baroclincity.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Complexities in the climate of the subpolar North Atlantic: a case study from the winter of 2007 (2011)
    Wiley
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    Publication Date: 2011-03-24
    Description: As a result of its high topography, Greenland significantly distorts the atmospheric flow affecting local as well as remote weather systems and, via air–sea interaction processes, the coupled climate system. During February and March 2007, a field campaign was carried out to investigate this as part of the international Greenland Flow Distortion Experiment (GFDex). The observational programme occurred during anomalous conditions, relative to the climatological mean, that favoured the formation of barrier flow along the southeastern coast of Greenland and easterly tip jets at Cape Farewell, Greenland's southernmost point, while inhibiting the formation of westerly tip jets in the same region. The North Atlantic Oscillation (NAO) index was positive, indicating a deep Icelandic Low. However, there was a southeastward shift in the low's centre and a more zonally oriented storm track that we propose to be the result of the concurrent positive phase of the East Atlantic (EA) teleconnection. Unlike the usual situation for an NAO positive state, there was also a warming in the lower troposphere over the Labrador Sea that we argue was the result of a relatively weak Canadian Polar Trough over the eastern Canadian Arctic. It is shown that consideration of the strength of the Canadian Polar Trough in conjunction with information on the phases of the NAO and EA provides for a qualitatively better representation of the state of the atmosphere over the subpolar North Atlantic during the winter of 2007, and by inference in general, than is possible via the NAO alone. Copyright © 2011 Royal Meteorological Society
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 10
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    Mechanisms controlling dissolved iron distribution in the North Pacific: A model study (2011)
    Wiley
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    Publication Date: 2011-07-22
    Description: Mechanisms controlling the dissolved iron distribution in the North Pacific are investigated using the Biogeochemical Elemental Cycling (BEC) model with a resolution of approximately 1° in latitude and longitude and 60 vertical levels. The model is able to reproduce the general distribution of iron as revealed in available field data: surface concentrations are generally below 0.2 nM; concentrations increase with depth; and values in the lower pycnocline are especially high in the northwestern Pacific and off the coast of California. Sensitivity experiments changing scavenging regimes and external iron sources indicate that lateral transport of sedimentary iron from continental margins into the open ocean causes the high concentrations in these regions. This offshore penetration only appears under a scavenging regime where iron has a relatively long residence time at high concentrations, namely, the order of years. Sedimentary iron is intensively supplied around continental margins, resulting in locally high concentrations; the residence time with respect to scavenging determines the horizontal scale of elevated iron concentrations. Budget analysis for iron reveals the processes by which sedimentary iron is transported to the open ocean. Horizontal mixing transports sedimentary iron from the boundary into alongshore currents, which then carry high iron concentrations into the open ocean in regions where the alongshore currents separate from the coast, most prominently in the northwestern Pacific and off of California.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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