Schweiger Axel

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Schweiger
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Axel
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  • Article
    Biophysical consequences of a relaxing Beaufort Gyre
    (American Geophysical Union, 2019-12-19) Zhang, Jinlun ; Spitz, Yvette H. ; Steele, Michael ; Ashjian, Carin J. ; Campbell, Robert G. ; Schweiger, Axel
    A biophysical model shows that Beaufort Gyre (BG) intensification in 2004–2016 is followed by relaxation in 2017–2018, based on a BG variability index. BG intensification leads to enhanced downwelling in the central Canada Basin (CCB) and upwelling along the coast. In the CCB, enhanced downwelling reduces nutrients, thus lowering primary productivity (PP) and plankton biomass. Enhanced upwelling along the coast and in parts of the Chukchi shelf/slope increases nutrients, leading to elevated PP/biomass in the Pacific Arctic Ocean (PAO) outside of the CCB. The overall PAO PP/biomass is dominated by the shelf/slope response and thus increases during BG intensification. As the BG relaxes in 2017–2018, these processes largely reverse, with increasing PP/biomass in the CCB and decreasing PP/biomass in most of the shelf/slope regions. Because the shelf/slope regions are much more productive than the CCB, BG relaxation has the tendency to reduce the overall production in the PAO.
  • Article
    Winter-to-summer transition of Arctic sea ice breakup and floe size distribution in the Beaufort Sea
    (University of California Press, 2017-07-26) Hwang, Byongjun ; Wilkinson, Jeremy P. ; Maksym, Ted ; Graber, Hans C. ; Schweiger, Axel ; Horvat, Christopher ; Perovich, Donald K. ; Arntsen, Alexandra ; Stanton, Timothy P. ; Ren, Jinchang ; Wadhams, Peter
    Breakup of the near-continuous winter sea ice into discrete summer ice floes is an important transition that dictates the evolution and fate of the marginal ice zone (MIZ) of the Arctic Ocean. During the winter of 2014, more than 50 autonomous drifting buoys were deployed in four separate clusters on the sea ice in the Beaufort Sea, as part of the Office of Naval Research MIZ program. These systems measured the ocean-ice-atmosphere properties at their location whilst the sea ice parameters in the surrounding area of these buoy clusters were continuously monitored by satellite TerraSAR-X Synthetic Aperture Radar. This approach provided a unique Lagrangian view of the winter-to-summer transition of sea ice breakup and floe size distribution at each cluster between March and August. The results show the critical timings of a) temporary breakup of winter sea ice coinciding with strong wind events and b) spring breakup (during surface melt, melt ponding and drainage) leading to distinctive summer ice floes. Importantly our results suggest that summer sea ice floe distribution is potentially affected by the state of winter sea ice, including the composition and fracturing (caused by deformation events) of winter sea ice, and that substantial mid-summer breakup of sea ice floes is likely linked to the timing of thermodynamic melt of sea ice in the area. As the rate of deformation and thermodynamic melt of sea ice has been increasing in the MIZ in the Beaufort Sea, our results suggest that these elevated factors would promote faster and more enhanced breakup of sea ice, leading to a higher melt rate of sea ice and thus a more rapid advance of the summer MIZ.
  • Article
    CryoSat-2 estimates of Arctic sea ice thickness and volume
    (John Wiley & Sons, 2013-02-28) Laxon, Seymour W. ; Giles, Katharine A. ; Ridout, Andy L. ; Wingham, Duncan J. ; Willatt, Rosemary ; Cullen, Robert ; Kwok, Ron ; Schweiger, Axel ; Zhang, Jinlun ; Haas, Christian ; Hendricks, Stefan ; Krishfield, Richard A. ; Kurtz, Nathan ; Farrell, Sinéad L. ; Davidson, Malcolm
    Satellite records show a decline in ice extent over more than three decades, with a record minimum in September 2012. Results from the Pan-Arctic Ice-Ocean Modelling and Assimilation system (PIOMAS) suggest that the decline in extent has been accompanied by a decline in volume, but this has not been confirmed by data. Using new data from the European Space Agency CryoSat-2 (CS-2) mission, validated with in situ data, we generate estimates of ice volume for the winters of 2010/11 and 2011/12. We compare these data with current estimates from PIOMAS and earlier (2003–8) estimates from the National Aeronautics and Space Administration ICESat mission. Between the ICESat and CryoSat-2 periods, the autumn volume declined by 4291 km3 and the winter volume by 1479 km3. This exceeds the decline in ice volume in the central Arctic from the PIOMAS model of 2644 km3 in the autumn, but is less than the 2091 km3 in winter, between the two time periods.
  • Article
    Melt pond conditions on declining arctic sea ice over 1979-2016: Model development, validation, and results
    (American Geophysical Union, 2018-10-18) Zhang, Jinlun ; Schweiger, Axel ; Webster, Melinda ; Light, Bonnie ; Steele, Michael ; Ashjian, Carin J. ; Campbell, Robert ; Spitz, Yvette H.
    A melt pond (MP) distribution equation has been developed and incorporated into the Marginal Ice‐Zone Modeling and Assimilation System to simulate Arctic MPs and sea ice over 1979–2016. The equation differs from previous MP models and yet benefits from previous studies for MP parameterizations as well as a range of observations for model calibration. Model results show higher magnitude of MP volume per unit ice area and area fraction in most of the Canada Basin and the East Siberian Sea and lower magnitude in the central Arctic. This is consistent with Moderate Resolution Imaging Spectroradiometer observations, evaluated with Measurements of Earth Data for Environmental Analysis (MEDEA) data, and closely related to top ice melt per unit ice area. The model simulates a decrease in the total Arctic sea ice volume and area, owing to a strong increase in bottom and lateral ice melt. The sea ice decline leads to a strong decrease in the total MP volume and area. However, the Arctic‐averaged MP volume per unit ice area and area fraction show weak, statistically insignificant downward trends, which is linked to the fact that MP water drainage per unit ice area is increasing. It is also linked to the fact that MP volume and area decrease relatively faster than ice area. This suggests that overall the actual MP conditions on ice have changed little in the past decades as the ice cover is retreating in response to Arctic warming, thus consistent with the Moderate Resolution Imaging Spectroradiometer observations that show no clear trend in MP area fraction over 2000–2011.
  • Article
    Heat stored in the Earth system: where does the energy go?
    (Copernicus Publications, 2020-09-07) von Schuckmann, Karina ; Cheng, Lijing ; Palmer, Matthew D. ; Hansen, James ; Tassone, Caterina ; Aicher, Valentin ; Adusumilli, Susheel ; Beltrami, Hugo ; Boyer, Tim ; Cuesta-Valero, Francisco José ; Desbruyeres, Damien ; Domingues, Catia M. ; García-García, Almudena ; Gentine, Pierre ; Gilson, John ; Gorfer, Maximilian ; Haimberger, Leopold ; Ishii, Masayoshi ; Johnson, Gregory C. ; Killick, Rachel E. ; King, Brian A. ; Kirchengast, Gottfried ; Kolodziejczyk, Nicolas ; Lyman, John ; Marzeion, Ben ; Mayer, Michael ; Monier, Maeva ; Monselesan, Didier Paolo ; Purkey, Sarah G. ; Roemmich, Dean ; Schweiger, Axel ; Seneviratne, Sonia I. ; Shepherd, Andrew ; Slater, Donald A. ; Steiner, Andrea K. ; Straneo, Fiammetta ; Timmermans, Mary-Louise ; Wijffels, Susan E.
    Human-induced atmospheric composition changes cause a radiative imbalance at the top of the atmosphere which is driving global warming. This Earth energy imbalance (EEI) is the most critical number defining the prospects for continued global warming and climate change. Understanding the heat gain of the Earth system – and particularly how much and where the heat is distributed – is fundamental to understanding how this affects warming ocean, atmosphere and land; rising surface temperature; sea level; and loss of grounded and floating ice, which are fundamental concerns for society. This study is a Global Climate Observing System (GCOS) concerted international effort to update the Earth heat inventory and presents an updated assessment of ocean warming estimates as well as new and updated estimates of heat gain in the atmosphere, cryosphere and land over the period 1960–2018. The study obtains a consistent long-term Earth system heat gain over the period 1971–2018, with a total heat gain of 358±37 ZJ, which is equivalent to a global heating rate of 0.47±0.1 W m−2. Over the period 1971–2018 (2010–2018), the majority of heat gain is reported for the global ocean with 89 % (90 %), with 52 % for both periods in the upper 700 m depth, 28 % (30 %) for the 700–2000 m depth layer and 9 % (8 %) below 2000 m depth. Heat gain over land amounts to 6 % (5 %) over these periods, 4 % (3 %) is available for the melting of grounded and floating ice, and 1 % (2 %) is available for atmospheric warming. Our results also show that EEI is not only continuing, but also increasing: the EEI amounts to 0.87±0.12 W m−2 during 2010–2018. Stabilization of climate, the goal of the universally agreed United Nations Framework Convention on Climate Change (UNFCCC) in 1992 and the Paris Agreement in 2015, requires that EEI be reduced to approximately zero to achieve Earth's system quasi-equilibrium. The amount of CO2 in the atmosphere would need to be reduced from 410 to 353 ppm to increase heat radiation to space by 0.87 W m−2, bringing Earth back towards energy balance. This simple number, EEI, is the most fundamental metric that the scientific community and public must be aware of as the measure of how well the world is doing in the task of bringing climate change under control, and we call for an implementation of the EEI into the global stocktake based on best available science. Continued quantification and reduced uncertainties in the Earth heat inventory can be best achieved through the maintenance of the current global climate observing system, its extension into areas of gaps in the sampling, and the establishment of an international framework for concerted multidisciplinary research of the Earth heat inventory as presented in this study. This Earth heat inventory is published at the German Climate Computing Centre (DKRZ, https://www.dkrz.de/, last access: 7 August 2020) under the DOI https://doi.org/10.26050/WDCC/GCOS_EHI_EXP_v2 (von Schuckmann et al., 2020).