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  • 1
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    Hunting a New Ocean Tracer (2008)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 89 (43).
    Details
    Publication Date: 2017-03-03
    Type: Article , NonPeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - without review
  • 2
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    Use of SF6 to estimate anthropogenic CO2 in the upper ocean (2008)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 113 . C04037.
    Details
    Publication Date: 2018-04-25
    Description: The highest concentrations of anthropogenic carbon (C_ant) are found in the upper layers of the world ocean. However, this is where seasonal variability of inorganic carbon and related parameters due to thermal and biological effects complicates use of back-calculation approaches for C ant . Tracer based approaches to C_ant estimation are unaffected by biological variability and have found wide application. However, slow-down, even reversal, of the atmospheric growth of chlorofluorocarbons (CFCs) restricts use of these tracers for C ant estimation for waters ventilated since the mid 1990s. Here we apply SF6, a tracer that continues to increase in the atmosphere, as a basis for the C_ant estimation, using samples collected in the midlatitude North Atlantic in 2004. C ant estimates derived from water mass transit time distributions (TTDs) calculated with SF6 are compared to those based on CFC-12. For recently ventilated waters (pCFC-12 〉 ∼450 ppt), the uncertainty of SF6 based estimates of C_ant is ∼6 μmol kg−1 less than that of CFC-12 based estimates. CFC-12 based estimates remain more reliable for older (deeper) water masses, as a result of the longer input history and more readily detectable concentrations of CFC-12. Historical data suggest that the near-surface saturation of CFC-12 has increased over time, in inverse proportion to its atmospheric growth rate. Use of a time-dependent saturation of CFC-12 in TTD calculations appears to provide more reliable estimation of C_ant .
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2007JC004416
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Inventory changes of anthropogenic carbon in the Atlantic between 1997 and 2003 (2009)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 23 (GB3010).
    Details
    Publication Date: 2018-03-20
    Description: The oceans absorb and store a significant portion of anthropogenic CO2 emissions, but large uncertainties remain in the quantification of this sink. An improved assessment of the present and future oceanic carbon sink is therefore necessary to provide recommendations for long‐term global carbon cycle and climate policies. The formation of North Atlantic Deep Water (NADW) is a unique fast track for transporting anthropogenic CO2 into the ocean's interior, making the deep waters rich in anthropogenic carbon. Thus the Atlantic is presently estimated to hold 38% of the oceanic anthropogenic CO2 inventory, although its volume makes up only 25% of the world ocean. Here we analyze the inventory change of anthropogenic CO2 in the Atlantic between 1997 and 2003 and its relationship to NADW formation. For the whole region between 20°S and 65°N the inventory amounts to 32.5 ± 9.5 Petagram carbon (Pg C) in 1997 and increases up to 36.0 ± 10.5 Pg C in 2003. This result is quite similar to earlier studies. Moreover, the overall increase of anthropogenic carbon is in close agreement with the expected change due to rising atmospheric CO2 levels of 1.69% a−1. On the other hand, when considering the subpolar region only, the results demonstrate that the recent weakening in the formation of Labrador Sea Water, a component of NADW, has already led to a decrease of the anthropogenic carbon inventory in this water mass. As a consequence, the overall inventory for the total water column in the western subpolar North Atlantic increased only by 2% between 1997 and 2003, much less than the 11% that would be expected from the increase in atmospheric CO2 levels.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008GB003311
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Consistency of TTO-NAS inorganic carbon data with modern measurements (2005)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 32 . L14618.
    Details
    Publication Date: 2018-03-28
    Description: We compare alkalinity and total dissolved inorganic carbon (DIC) measurements made during the Transient Tracers in the Ocean, North Atlantic Study (TTO‐NAS) in 1981 with modern measurements from a TTO reoccupation cruise in 2004 (M60/5). We find that the TTO‐NAS alkalinity values are 3.6 ± 2.3 μmol kg−1 higher than modern alkalinity data tied to Certified Reference Materials. The TTO‐NAS DIC values re‐calculated from original alkalinity and discrete‐pCO2 data using currently accepted constants are 3.8 μmol kg−1 higher than those reported in the revised TTO data set. This difference is reduced to 0.7 μmol kg−1 when our suggested correction to the TTO‐NAS alkalinity is applied. These re‐calculated DIC values are 2.4 μmol kg−1 too low relative to contemporaneous measurements made by the vacuum extraction/manometric Certified method. Application of this correction brings the TTO data into almost perfect agreement with modern measurements for slowly‐ventilated deep water of the eastern Atlantic.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2005GL023248
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Spreading of overflow water from the Greenland to the Labrador Sea (2005)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 32 (10). L10605.
    Details
    Publication Date: 2018-03-28
    Description: In 1996, about 320 kg of SF6 were introduced in the center of the Greenland Sea gyre. We use this signal together with the CFC distribution to follow the spreading of Greenland gyre water from the Denmark Strait through the Irminger Basin and the Labrador Sea to the Grand Banks. In the summer of 2003 Denmark Strait Overflow Water tagged with deliberately released SF6 could be traced throughout the Irminger Basin to the central Labrador Sea, confirming that water with potential density of 28.045 contributes to the Denmark Strait Overflow. The upper limit of the transfer time from the central Greenland Sea to the Labrador Sea was found to be 7 years. This study suggests that roughly 4 kg of excess SF6 has been transported over the Denmark Strait and confirm earlier reported transport through the Faroe Bank Channel. These results should be considered when using SF6 as a transient tracer.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2005GL022700
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Changes of anthropogenic CO〈sub〉2〈/sub〉 and CFCs in the North Atlantic between 1981 and 2004 (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 (4). GB4017.
    Details
    Publication Date: 2019-09-23
    Description: We compare total dissolved inorganic carbon (DIC) and chlorofluorocarbon (CFC) measurements in the northwest Atlantic made during the Transient Tracers in the Ocean, North Atlantic Study (TTO‐NAS) in 1981 with modern measurements from a cruise in 2004. The observed changes in the DIC and CFC fields are compared to those predicted from an eddy‐permitting ocean circulation model. The rapid, but time‐variable, atmospheric CFC increase in relation to the relatively steady anthropogenic CO2 increase influences the relationship between the observed uptake of DIC and CFC. We demonstrate the importance of ocean mixing in the calculation of anthropogenic CO2 (Cant) based on transient tracer data by comparing our observations to a “no‐mixing” scenario. We further find that the Cant is in transient steady state in the North Atlantic; that is, the Cant concentration increases proportionally over time through the whole water column in a manner that is directly related to the time‐dependent surface concentration.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2006GB002695
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Ventilation of the Arctic Ocean: Mean ages and inventories of anthropogenic CO2 and CFC-11 (2009)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 114 . C01002.
    Details
    Publication Date: 2019-09-23
    Description: The Arctic Ocean constitutes a large body of water that is still relatively poorly surveyed because of logistical difficulties, although the importance of the Arctic Ocean for global circulation and climate is widely recognized. For instance, the concentration and inventory of anthropogenic CO2 (C ant) in the Arctic Ocean are not properly known despite its relatively large volume of well-ventilated waters. In this work, we have synthesized available transient tracer measurements (e.g., CFCs and SF6) made during more than two decades by the authors. The tracer data are used to estimate the ventilation of the Arctic Ocean, to infer deep-water pathways, and to estimate the Arctic Ocean inventory of C ant. For these calculations, we used the transit time distribution (TTD) concept that makes tracer measurements collected over several decades comparable with each other. The bottom water in the Arctic Ocean has CFC values close to the detection limit, with somewhat higher values in the Eurasian Basin. The ventilation time for the intermediate water column is shorter in the Eurasian Basin (∼200 years) than in the Canadian Basin (∼300 years). We calculate the Arctic Ocean C ant inventory range to be 2.5 to 3.3 Pg-C, normalized to 2005, i.e., ∼2% of the global ocean C ant inventory despite being composed of only ∼1% of the global ocean volume. In a similar fashion, we use the TTD field to calculate the Arctic Ocean inventory of CFC-11 to be 26.2 ± 2.6 × 106 moles for year 1994, which is ∼5% of the global ocean CFC-11 inventory
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1029/2008JC004868
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Deoxygenation in the oxygen minimum zone of the eastern tropical North Atlantic (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L20607.
    Details
    Publication Date: 2019-09-23
    Description: Observations and model results both indicate increasing oxygen minimum zones (OMZ) in the tropical oceans. Here we report on record low dissolved oxygen minimum concentrations in the eastern tropical North Atlantic in fall of 2008, with less than 40 mu mol kg(-1) in the core of the OMZ. There we find a deoxygenation rate of similar to 0.5 mu mol kg(-1) a(-1) during the last decades on two repeat sections at 7.5 and 11 degrees N. The potential temperature and salinity in the surface and central water layers increased on both sections compared to previous observations. However, in contrast to the oxygen decrease in the core of the OMZ, increasing oxygen concentrations were observed in the central water layer above the OMZ. The observed deoxygenation was thus restricted to the core of the oxygen minimum layer. It remains unclear whether the vertical expansion of the oxygen minimum represents a long time trend or decadal variations
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009GL039593
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    North Atlantic production of nitrous oxide in the context of changing atmospheric levels (2009)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 23 . GB4015.
    Details
    Publication Date: 2019-09-23
    Description: We use transit time distributions calculated from tracer data together with in situ measurements of N(2)O to estimate the concentration of biologically produced N(2)O ([N(2)O](xs)) and N(2)O production rates in the central North Atlantic Ocean. Our approach to estimation of N(2)O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass. We find that previously used approaches overestimate the oceanic equilibrium N(2)O concentrations by 8-13% and thus underestimate the strength of N(2)O sources in large parts of the water column. Thus the quantitative characteristics of the [N(2)O](xs)/AOU relationship used as an indicator of nitrification are distorted. We developed a new parameterization of N(2)O production during nitrification depending linearly on AOU and exponentially on temperature and depth, which can be applied to calculate N(2)O production due to nitrification in the entire ocean including oxygen minimum zones.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009GB003472
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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