Nutrients that limit growth in the ocean Laura A. Bristow, Wiebke Mohr, Soeren Ahmerkamp, Marcel M.M. Kuypers  Current Biology  Volume 27, Issue 11, Pages R474-R478 (June 2017) DOI: 10.1016/j.cub.2017.03.030 Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 1 Patterns of growth related to nutrient limitation. A) Distribution of surface chlorophyll a (μg per L). White arrows depict the location and circulation direction of the open ocean gyres. B) Surface nitrate concentrations (μmol per L) and approximate locations of the high-nutrient low-chlorophyll (HNLC) regions. C) N∗ (calculated as N∗ = (NO3- + NO2-) – 16∗P + 2.9 μmol per kg; Gruber and Sarmiento, 1997) and oxygen concentrations (black contour lines) at 90 m water depth. This depth was chosen to highlight the shelf regions and OMZs; however, positive N∗ as a result of N2 fixation is often not observed at this depth. D) Depth-integrated N2-fixation rates (circles, scale bar to the right of the panel; μmol per m2 per day; modified from Luo et al., 2012, zero values excluded), with blue shading showing regions of dust deposition (scale bar below; adapted from Jickells et al., 2005). Data in panels A–C from World Ocean Atlas, 2013 v2. Current Biology 2017 27, R474-R478DOI: (10.1016/j.cub.2017.03.030) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 2 Schematic of the nitrogen cycle in the open and coastal ocean. Schematic showing nitrogen cycle processes occurring in the open ocean (left) and the coastal ocean, with an oxygen minimum zone (right). Depth profiles (far left) show typical distributions of light and nutrients (nitrate and phosphate) in the open ocean that can lead to the formation of a deep chlorophyll a maximum (green shading). The processes depicted in the open ocean also occur in the coastal ocean; in the presence of an OMZ, denitrification and anammox lead to nitrogen loss. Independent of an OMZ, sedimentary denitrification results in significant nitrogen loss. The processes of anammox (yellow), assimilation (green), denitrification (orange) and nitrification (blue) are shown by arrows. Nitrate, NO3-; iron, Fe2+/3+; phosphate, PO43-; ammonium, NH4+; nitrite, NO2-; nitrous oxide, N2O; nitric oxide, NO; organic matter, OM. Current Biology 2017 27, R474-R478DOI: (10.1016/j.cub.2017.03.030) Copyright © 2017 Elsevier Ltd Terms and Conditions