Changes in the physical environment associated with eastern Pacific (EP)‐El Niño and central Pacific (CP)‐El Niño events affect the biological response in the equatorial Pacific Ocean differently. However, such responses have not been adequately investigated, especially in terms of the relevant physical processes. This paper addresses the mechanistic differences in the biological response of the equatorial Pacific Ocean during the strongest CP‐ and EP‐El Niño to date (i.e., 1997–98 EP‐El Niño and 2009–10 CP‐El Niño) using satellite data and water mass pathway analysis based on an ocean reanalysis product. The 1997–98 EP‐El Niño was associated with a larger reduction of chlorophyll‐a (chl‐a) in the eastern equatorial Pacific (EEP) and the 2009–10 CP‐El Niño was associated with a larger reduction of chl‐a in the central equatorial Pacific (CEP). These biological responses were dependent on the strength and extent of westerly wind anomalies and their impact on horizontal and vertical processes. Horizontal advection was the primary contributor to differences in chl‐a between the two El Niño events in the CEP, whereas vertical advection and mixing were the dominant processes in the EEP.

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[1] El Niño events are known to strongly affect biological production and ecosystem structure in the tropical Pacific. Understanding and predicting biological processes in this area are hampered because the existing in situ observing system focuses primarily on physical measurements and does not observe key biological parameters; the only high spatial and temporal resolution biology-related observations are from the global array of ocean color satellites which provide an estimate of surface chlorophyll concentrations only. Since the 1990s, an apparent shift of the El Niño maximum sea-surface temperature (SST) warm anomaly from the eastern to the central equatorial Pacific has frequently been observed. Satellite observations show significant changes in chlorophyll-a (Chl-a), new production (NP) and total primary production (PP) in the equatorial Pacific associated with these new central Pacific (CP) El Niño events (also called El Niño Modoki) relative to eastern Pacific El Niños. During CP-El Niños, NP, Chl-a and PP in the central basin are depressed relative to EP-El Niños and lower values of Chl-a and PP coincide spatially with higher SST in the central Pacific. While surface Chl-a, and integrated NP and PP over the entire equatorial band, decrease during both CP and EP-El Niños, the magnitude of this decrease seems to depend more on the intensity than type of event. The changing spatial patterns have significant implications for equatorial biological dynamics if, as has been suggested, CP-El Niños increase in frequency in the future. Citation:

A combination of ship, buoy, and satellite observations in the tropical Pacific during the period from 1992 to 2000 provides a basin-scale perspective on the net effects of El Niño and La Niña on biogeochemical cycles. New biological production during the 1997-99 El Niño/La Niña period varied by more than a factor of 2. The resulting interannual changes in global carbon sequestration associated with the El Niño/La Niña cycle contributed to the largest known natural perturbation of the global carbon cycle over these time scales.

The ocean plays a major role in the global carbon cycle through the atmosphere‐ocean partitioning of atmospheric carbon dioxide. Rain alters the physics and carbon chemistry at the ocean surface to increase the amount of CO2 taken up by the ocean. This paper presents the results of a preliminary study wherein rain measurements in the western equatorial Pacific are used to determine the enhanced transfer, chemical dilution and deposition effects of rain on air‐sea CO2 exchange. Including these processes, the western equatorial Pacific CO2 flux is modified from an ocean source of +0.019 mol CO2 m−2 yr−1 to an ocean sink of −0.078 mol CO2 m−2 yr−1. This new understanding of rain effects changes the ocean's role in the global carbon budget, particularly in regions with low winds and high precipitation.

EXECUTIVE SUMMARYCoastal environments are an important component of the global carbon cycle, and probably more vulnerable than the open ocean to anthropogenic forcings. Due to strong spatial heterogeneity and temporal variability, carbon flows in coastal environments are poorly constrained. Hence, an integrated, international, and interdisciplinary program of ship-based hydrography, Voluntary Observing Ship (VOS) lines, time-series moorings, floats, gliders, and autonomous surface vessels with sensors for pCO 2 and ancillary variables are recommended to better understand present day carbon cycle dynamics, quantify air-sea CO 2 fluxes, and determine future long-term trends of CO 2 in response to global change forcings (changes in river inputs, in the hydrological cycle, in circulation, sea-ice retreat, expanding oxygen minimum zones, ocean acidification, …) in the coastal oceans. Integration at the international level is also required for data archiving, management, and synthesis that will require multi-scale approaches including the development of biogeochemical models and use of remotely sensed parameters. The total cost of these observational efforts is estimated at about 50 million US dollars per year.

Abstract. A quantification of carbon fluxes in the coastal ocean and across its boundaries with the atmosphere, land, and the open ocean is important for assessing the current state and projecting future trends in ocean carbon uptake and coastal ocean acidification, but this is currently a missing component of global carbon budgeting. This synthesis reviews recent progress in characterizing these carbon fluxes for the North American coastal ocean. Several observing networks and high-resolution regional models are now available. Recent efforts have focused primarily on quantifying the net air–sea exchange of carbon dioxide (CO2). Some studies have estimated other key fluxes, such as the exchange of organic and inorganic carbon between shelves and the open ocean. Available estimates of air–sea CO2 flux, informed by more than a decade of observations, indicate that the North American Exclusive Economic Zone (EEZ) acts as a sink of 160±80 Tg C yr−1, although this flux is not well constrained. The Arctic and sub-Arctic, mid-latitude Atlantic, and mid-latitude Pacific portions of the EEZ account for 104, 62, and −3.7 Tg C yr−1, respectively, while making up 51 %, 25 %, and 24 % of the total area, respectively. Combining the net uptake of 160±80 Tg C yr−1 with an estimated carbon input from land of 106±30 Tg C yr−1 minus an estimated burial of 65±55 Tg C yr−1 and an estimated accumulation of dissolved carbon in EEZ waters of 50±25 Tg C yr−1 implies a carbon export of 151±105 Tg C yr−1 to the open ocean. The increasing concentration of inorganic carbon in coastal and open-ocean waters leads to ocean acidification. As a result, conditions favoring the dissolution of calcium carbonate occur regularly in subsurface coastal waters in the Arctic, which are naturally prone to low pH, and the North Pacific, where upwelling of deep, carbon-rich waters has intensified. Expanded monitoring and extension of existing model capabilities are required to provide more reliable coastal carbon budgets, projections of future states of the coastal ocean, and quantification of anthropogenic carbon contributions.

Diverse instruments, both custom built and commercially available, have been used to measure the properties of the aqueous CO 2 system in seawater at differing levels of autonomy (automated benchtop, continuous underway, autonomous in situ). In this review, we compare the capabilities of commercially available instruments with the needs of oceanographers in order to highlight major shortfalls in the state-of-the art instrumentation broadly available to the ocean acidification (OA) scientific community. In addition, we describe community surveys that identify needs for continued development and refinement of sensor and instrument technologies, expansion of programs that provide Certified Reference Materials, development of best practices documentation for autonomous sensors, and continued and expanded sensor intercomparison experiments.