No Thumbnail Available
Now showing 1 - 5 of 5
ArticleArctic Ocean basin liquid freshwater storage trend 1992–2012(John Wiley & Sons, 2014-02-12) Rabe, Benjamin ; Karcher, Michael ; Kauker, Frank ; Schauer, Ursula ; Toole, John M. ; Krishfield, Richard A. ; Pisarev, Sergey ; Kikuchi, Takashi ; Su, J.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 trend was 600±300 km3 yr−1. A numerical model agrees very well with the observed freshwater changes. A decrease in salinity made up about two thirds of the freshwater trend and a thickening of the upper layer up to one third. The Arctic Ocean Oscillation index, a measure for the regional wind stress curl, correlated well with our freshwater time series. No clear relation to Arctic Oscillation or Arctic Dipole indices could be found. Following other observational studies, an increased Bering Strait freshwater import to the Arctic Ocean, a decreased Davis Strait export, and enhanced net sea ice melt could have played an important role in the freshwater trend we observed.
PreprintDistribution of Pb-210 and Po-210 in the arctic water column during the 2007 sea-ice minimum: Particle export in the ice-covered basins.(Elsevier, 2018-10-22) Roca-Martí, Montserrat ; Puigcorbé, Viena ; Friedrich, Jana ; Rutgers van der Loeff, Michiel ; Rabe, Benjamin ; Korhonen, Meri ; Cámara Mor, Patricia ; Garcia-Orellana, Jordi ; Masqué, Pere210Pb and 210Po are naturally occurring radionuclides that are commonly used as a proxy for particle and carbon export. In this study, the distribution of the 210Po/210Pb pair was investigated in the water column of the Barents, Kara and Laptev Seas and the Nansen, Amundsen and Makarov Basins in order to understand the particle dynamics in the Arctic Ocean during the 2007 sea-ice minimum (August-September). Minimum activities of total 210Pb and 210Po were found in the upper and lower haloclines (approx. 60-130 m), which are partly attributed to particle scavenging over the shelves, boundary current transport and subsequent advection of the water with low 210Pb and 210Po activities into the central Arctic. Widespread and substantial (>50%) deficits of 210Po with respect to 210Pb were detected from surface waters to 200 m on the shelves, but also in the basins. This was particularly important in the Makarov Basin where, despite very low chlorophyll-a levels, estimates of annual new primary production were three times higher than in the Eurasian Basin. In the Nansen, Amundsen and Makarov 32 Basins, estimates of annual new primary production correlated with the deficits of 210Po in the upper 200 m of the water column, suggesting that in situ production and subsequent export of biogenic material were the mechanisms that controlled the removal of 210Po in the central Arctic. Unlike 210Po, 234Th deficits measured during the same expedition were found to be very small and not significant below 25 m in the basins (Cai et al., 2010), which indicates, given the shorter half-life of 234Th, that particle export fluxes in the central Arctic would have been higher before July-August in 2007 than later in the season.
ArticleEvolving the physical global ocean observing system for research and application services through international coordination(Frontiers Media, 2019-08-06) Sloyan, Bernadette M. ; Wilkin, John L. ; Hill, Katherine Louise ; Chidichimo, Maria Paz ; Cronin, Meghan F. ; Johannessen, Johnny A. ; Karstensen, Johannes ; Krug, Marjolaine ; Lee, Tong ; Oka, Eitarou ; Palmer, Matthew D. ; Rabe, Benjamin ; Speich, Sabrina ; von Schuckmann, Karina ; Weller, Robert A. ; Yu, WeidongClimate change and variability are major societal challenges, and the ocean is an integral part of this complex and variable system. Key to the understanding of the ocean’s role in the Earth’s climate system is the study of ocean and sea-ice physical processes, including its interactions with the atmosphere, cryosphere, land, and biosphere. These processes include those linked to ocean circulation; the storage and redistribution of heat, carbon, salt and other water properties; and air-sea exchanges of heat, momentum, freshwater, carbon, and other gasses. Measurements of ocean physics variables are fundamental to reliable earth prediction systems for a range of applications and users. In addition, knowledge of the physical environment is fundamental to growing understanding of the ocean’s biogeochemistry and biological/ecosystem variability and function. Through the progress from OceanObs’99 to OceanObs’09, the ocean observing system has evolved from a platform centric perspective to an integrated observing system. The challenge now is for the observing system to evolve to respond to an increasingly diverse end user group. The Ocean Observations Physics and Climate panel (OOPC), formed in 1995, has undertaken many activities that led to observing system-related agreements. Here, OOPC will explore the opportunities and challenges for the development of a fit-for-purpose, sustained and prioritized ocean observing system, focusing on physical variables that maximize support for fundamental research, climate monitoring, forecasting on different timescales, and society. OOPC recommendations are guided by the Framework for Ocean Observing which emphasizes identifying user requirements by considering time and space scales of the Essential Ocean Variables. This approach provides a framework for reviewing the adequacy of the observing system, looking for synergies in delivering an integrated observing system for a range of applications and focusing innovation in areas where existing technologies do not meet these requirements.
ArticleAdequacy of the ocean observation system for quantifying regional heat and freshwater storage and change(Frontiers Media, 2019-08-29) Palmer, Matthew D. ; Durack, Paul J. ; Chidichimo, Maria Paz ; Church, John A. ; Cravatte, Sophie ; Hill, Katherine Louise ; Johannessen, Johnny A. ; Karstensen, Johannes ; Lee, Tong ; Legler, David ; Mazloff, Matthew R. ; Oka, Eitarou ; Purkey, Sarah G. ; Rabe, Benjamin ; Sallee, Jean-Baptiste ; Sloyan, Bernadette M. ; Speich, Sabrina ; von Schuckmann, Karina ; Willis, Josh ; Wijffels, Susan E.Considerable advances in the global ocean observing system over the last two decades offers an opportunity to provide more quantitative information on changes in heat and freshwater storage. Variations in these storage terms can arise through internal variability and also the response of the ocean to anthropogenic climate change. Disentangling these competing influences on the regional patterns of change and elucidating their governing processes remains an outstanding scientific challenge. This challenge is compounded by instrumental and sampling uncertainties. The combined use of ocean observations and model simulations is the most viable method to assess the forced signal from noise and ascertain the primary drivers of variability and change. Moreover, this approach offers the potential for improved seasonal-to-decadal predictions and the possibility to develop powerful multi-variate constraints on climate model future projections. Regional heat storage changes dominate the steric contribution to sea level rise over most of the ocean and are vital to understanding both global and regional heat budgets. Variations in regional freshwater storage are particularly relevant to our understanding of changes in the hydrological cycle and can potentially be used to verify local ocean mass addition from terrestrial and cryospheric systems associated with contemporary sea level rise. This White Paper will examine the ability of the current ocean observing system to quantify changes in regional heat and freshwater storage. In particular we will seek to answer the question: What time and space scales are currently resolved in different regions of the global oceans? In light of some of the key scientific questions, we will discuss the requirements for measurement accuracy, sampling, and coverage as well as the synergies that can be leveraged by more comprehensively analyzing the multi-variable arrays provided by the integrated observing system.
PreprintAn assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006-2008 period( 2010-12-10) Rabe, Benjamin ; Karcher, Michael ; Schauer, Ursula ; Toole, John M. ; Krishfield, Richard A. ; Pisarev, Sergey ; Kauker, Frank ; Gerdes, Rudiger ; Kikuchi, TakashiUnprecedented 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 1992−1999, LFW content relative to a salinity of 35 in the layer from the surface to the 34 isohaline increased by 8400 ± 2000 km3 in the Arctic Ocean (water depth greater than 500m). This is close to the annual export of freshwater (liquid and solid) from the Arctic Ocean reported in the literature. Observations and a model simulation show regional variations in LFW were both due to changes in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a mean freshening of the water column above this depth, associated with an increased net sea ice melt and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a quarter of the salinity contribution, and non-linear effects due to both factors were negligible.