Nitrogen fixation rates in a cyclone-anticyclone eddy pair in the North Pacific Subtropical Gyre (Cruise KOK1607)

Surface N₂ fixation rates were measured in the center of a cyclonic eddy (23.74°N, 157.39°W), an anticyclonic eddy (22.94°N, 155.95°W), and an additional station between the two eddies (23.44°N, 156.78°W) during May 2016. Seawater was collected from 25 m and sampled into 4.4 L bottles, spiked with ¹⁵N₂-enriched seawater, and incubated in surface-seawater cooled, flow-through, deck-board incubators fitted with screening to reproduce in situ light conditions. These incubations were conducted during the day (10 h incubation, 08:00-18:00 local time) and at night (6 h incubation, 22:00-04:00 local time), using seawater from separate CTD casts prior to each incubation. Times provided are the average time of each incubation. Details on ¹⁵N₂-enriched seawater preparation and other methodological details for the rate measurements are provided in Böttjer et al. (2017, <em>Limnology and Oceanography</em>, doi: 10.1002/lno.10386). Additional physical and biogeochemical data collected on cruise KOK1607 are available online: http://scope.soest.hawaii.edu/data/hoelegacy/data/2016年5月，研究人员于气旋涡旋（23.74°N，157.39°W）中心、反气旋涡旋（22.94°N，155.95°W）中心，以及两涡旋间的额外站位（23.44°N，156.78°W）测定了表层固氮（N₂ fixation）速率。研究人员从25米水层采集海水，将其分装至4.4 L培养瓶中，掺入¹⁵N₂富集海水（¹⁵N₂-enriched seawater），随后置于配备遮光网以模拟原位光照条件的表层海水冷却流通式甲板培养箱中开展培养。本次培养分为日间（培养时长10小时，当地时间08:00-18:00）与夜间（培养时长6小时，当地时间22:00-04:00）两组，每组培养前均使用独立CTD（Conductivity-Temperature-Depth，电导率-温度-深度仪）站位采集的海水。文中给出的时长为各次培养的平均时长。关于¹⁵N₂富集海水的制备方法及固氮速率测定的其他实验细节，详见Böttjer等人2017年发表于《Limnology and Oceanography》（湖沼学与海洋学）的论文，DOI: 10.1002/lno.10386。本次KOK1607航次采集的其余物理与生物地球化学数据可在线获取：http://scope.soest.hawaii.edu/data/hoelegacy/data/