Vertical decoupling of nitrate assimilation and nitrification in the Sargasso Sea

被引:42
作者
Fawcett, Sarah E. [1 ]
Ward, Bess B. [1 ]
Lomas, Michael W. [2 ]
Sigman, Daniel M. [1 ]
机构
[1] Princeton Univ, Dept Geosci, Princeton, NJ 08544 USA
[2] Bigelow Lab Ocean Sci, East Boothbay, ME 04544 USA
基金
美国国家科学基金会;
关键词
Nitrate assimilation; Nitrification; Dual isotopes of nitrate; Sargasso Sea; Nitrite removal; Organic carbon export; MARINE NITRIFYING BACTERIA; OXYGEN ISOTOPIC COMPOSITION; ATLANTIC TIME-SERIES; PRIMARY NITRITE MAXIMUM; ORGANIC-MATTER; MIXED-LAYER; NANOMOLAR CONCENTRATIONS; AMMONIUM ASSIMILATION; DENITRIFIER METHOD; OXIDATION RATES;
D O I
10.1016/j.dsr.2015.05.004
中图分类号
P7 [海洋学];
学科分类号
0707 ;
摘要
The fraction of phytoplankton growth that leads to the rain of organic carbon out of the sunlit surface ocean ("export production") is central to the ocean's sequestration of atmospheric carbon dioxide. Nitrate assimilation has long been taken as a measure of export production; however, this has recently been questioned by suggestions that much of the nitrate in the sunlit layer (the "euphotic zone") originates from biological nitrogen (N) already in surface waters. This view has been supported by recent observations of euphotic zone nitrate elevated in delta O-18 relative to its delta N-15, taken as indicative of nitrification (the oxidation of recycled ammonium to nitrite and then nitrate). To evaluate the potential importance of nitrification in the Sargasso Sea euphotic zone, we measured the delta N-15 and delta O-18 of seawater nitrate for samples with >= 0.2 mu M nitrate collected on 18 cruises in the Sargasso Sea, and here we present the first large data set to correct for the low but often measurable concentrations of nitrite. Regardless of season, nitrate (i.e., nitrate-only rather than nitrate + nitrite as is commonly reported) delta N-15 and delta O-18 increase in unison from below the base of the euphotic zone toward the surface. This pattern derives from nitrate assimilation by phytoplankton, implying that nitrification is much slower than the upward transport of nitrate into the lower Sargasso Sea euphotic zone. In the twilight zone below the euphotic zone, we observe a rise in nitrate delta O-18 (relative to deeper waters) that is not accompanied by a rise in delta N-15, suggesting nitrification co-occurring with nitrate assimilation. Nitrification, therefore, does not appear to occur in euphotic zone waters overlapping with nitrate assimilation only in the similar to 150 m-thick twilight zone layer below it. In net, the data argue for a simpler N cycle for the Sargasso Sea euphotic zone than has recently been suggested, with the rate of euphotic zone nitrate assimilation approximating that of organic carbon export to the deep ocean. (C) 2015 Elsevier Ltd. All rights reserved.
引用
收藏
页码:64 / 72
页数:9
相关论文
共 76 条
  • [41] N isotopic composition of dissolved organic nitrogen and nitrate at the Bermuda Atlantic time-series study site
    Knapp, AN
    Sigman, DM
    Lipschultz, F
    [J]. GLOBAL BIOGEOCHEMICAL CYCLES, 2005, 19 (01) : 1 - 15
  • [42] Nitrate isotopic composition between Bermuda and Puerto Rico:: Implications for N2 fixation in the Atlantic Ocean
    Knapp, Angela N.
    DiFiore, Peter J.
    Deutsch, Curtis
    Sigman, Daniel M.
    Lipschultz, Fredric
    [J]. GLOBAL BIOGEOCHEMICAL CYCLES, 2008, 22 (03)
  • [43] Isolation of an autotrophic ammonia-oxidizing marine archaeon
    Könneke, M
    Bernhard, AE
    de la Torre, JR
    Walker, CB
    Waterbury, JB
    Stahl, DA
    [J]. NATURE, 2005, 437 (7058) : 543 - 546
  • [44] Global gridded data set of the oxygen isotopic composition in seawater
    LeGrande, Allegra N.
    Schmidt, Gavin A.
    [J]. GEOPHYSICAL RESEARCH LETTERS, 2006, 33 (12)
  • [45] A time-series assessment of the nitrogen cycle at BATS
    Lipschultz, F
    [J]. DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 2001, 48 (8-9) : 1897 - 1924
  • [46] Concentration dependent nitrogen isotope fractionation during ammonium uptake by phytoplankton under an algal bloom condition in the Danshuei estuary, northern Taiwan
    Liu, Kon-Kee
    Kao, Shuh-Ji
    Chiang, Kuo-Ping
    Gong, Gwo-Ching
    Chang, Jeng
    Cheng, Jun-Shiang
    Lan, Cheng-You
    [J]. MARINE CHEMISTRY, 2013, 157 : 242 - 252
  • [47] Two decades and counting: 24-years of sustained open ocean biogeochemical measurements in the Sargasso Sea
    Lomas, M. W.
    Bates, N. R.
    Johnson, R. J.
    Knap, A. H.
    Steinberg, D. K.
    Carlson, C. A.
    [J]. DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 2013, 93 : 16 - 32
  • [48] Biogeochemical responses to late-winter storms in the Sargasso Sea, I-Pulses of primary and new production
    Lomas, M. W.
    Lipschultz, F.
    Nelson, D. M.
    Krause, J. W.
    Bates, N. R.
    [J]. DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS, 2009, 56 (06) : 843 - 860
  • [49] Forming the primary nitrite maximum: Nitrifiers or phytoplankton?
    Lomas, Michael W.
    Lipschultz, Fredric
    [J]. LIMNOLOGY AND OCEANOGRAPHY, 2006, 51 (05) : 2453 - 2467
  • [50] Impact of ocean phytoplankton diversity on phosphate uptake
    Lomas, Michael W.
    Bonachela, Juan A.
    Levin, Simon A.
    Martiny, Adam C.
    [J]. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 2014, 111 (49) : 17540 - 17545