Global overturning circulation partitions the deep ocean into regions, each with different physicochemical characteristics, but the extent to which these water masses represent distinct ecosystems remains unknown. In this work, we integrate extensive genomic information with hydrography and water mass age to delineate microbial taxonomic and functional boundaries across the South Pacific. Prokaryotic richness steeply increases with depth in the surface ocean, which forms a so-called phylocline, below which, richness is consistently high, dipping slightly in highly aged water. Reconstructed genomes self-organize into six spatially distinct taxonomic cohorts and 10 functionally distinct biomes that are primarily structured by wind-driven circulation at the surface and density-driven circulation at depth. Overall, water physicochemistry, modulated at depth by water age, drives microbial diversity patterns and functional potential in the pelagic ocean.

Nitrous oxide (N2O) is a potent greenhouse gas and ozone depleting substance, with the ocean accounting for about one third of global emissions. In marine environments, a significant amount of N2O is produced by biological processes in Oxygen Deficient Zones (ODZs). While recent technological advances are making surface N2O concentration more available, high temporal and spatial resolution water-column N2O concentration data are relatively scarce, limiting global N2O ocean models’ predictive capability. We present a N2O concentration, stable isotopic composition and isotopomer dataset of unprecedently large spatial coverage and depth resolution in the broader Pacific, crossing both the eastern tropical South and North Pacific Ocean ODZs collected as part of the GO-SHIP P18 repeat hydrography program in 2016/2017. We complement these data with dissolved gases (nitrogen, oxygen, argon) and nitrate isotope data to investigate the pathways controlling N2O production in relation to apparent oxygen utilization and fixed nitrogen loss. N2O yield significantly increased under low oxygen conditions near the ODZs. Keeling plot analysis revealed different N2O sources above the ODZs under different oxygen regimes. Our stable isotopic data and relationships between the N2O added by microbial processes (ΔN2O) and dissolved inorganic nitrogen (DIN) deficit confirm increased N2O production by denitrification under low oxygen conditions near the oxycline where the largest N2O accumulations were observed. The slope for δ18O-N2O versus site preference (SP, the difference between the central (α) and outer (β) N atoms in the linear N2O molecule) in the eastern tropical North Pacific ODZ was lower than expected for pure N2O reduction, likely because of the observed decrease in δ15Nβ. This trend is consistent with prior ODZ studies and attributed to concurrent production of N2O from nitrite with a low δ15N or denitrification with a SP >0‰. We estimated apparent isotope effects for N2O consumption in the ETNP ODZ of 3.6‰ for 15Nbulk, 9.4‰ for 15Nα, -2.3‰ for 15Nβ, 12.0‰ for 18O, and 11.7‰ for SP. These values were generally within ranges previously reported for previous laboratory and field experiments.

We use a nutrient-ratio budget method to investigate the relative importance of different nutrient source and sink terms at time-series Station ALOHA and Bermuda Atlantic Time-series Study (BATS) in the North Pacific and North Atlantic subtropical gyres, respectively. At mean state conditions over annual and multi-year time scales, vertical phosphate (PO43-) supply from the subsurface accounts for similar to 60% of the total phosphorus supply at both sites. Dissolved organic matter transport and zooplankton excretion are more important phosphorous export pathways than sinking particles at Station ALOHA and BATS. The nutrient-ratio budget approach provides quantitative, observation-based constraints on nutrient sources and sinks in the surface ocean, which helps improve our understanding of the biological carbon pump in oligotrophic oceans.

The ocean is warming, acidifying, and losing oxygen. The Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) carries out repeat hydrographic surveys along specified transects throughout all ocean basins to allow accurate and precise quantification of changes in variables such as temperature, salinity, carbon, oxygen, nutrients, velocity, and anthropogenic tracers, and uses these observations to understand ventilation patterns, deoxygenation, heat uptake, ocean carbon content, and changes in circulation. GO-SHIP provides global, full-depth, gold-standard data for model validation and calibration of autonomous sensors, including Argo. The Pacific Marine Environmental Laboratory, through sustained funding from NOAA, has developed methods to measure several of the variables routinely sampled through GO-SHIP and is a core contributor to these repeat hydrographic cruises.

The 13C/12C of dissolved inorganic carbon (δ13C DIC ) carries valuable information on ocean biological C-cycling, air-sea CO2 exchange, and circulation. Paleo-reconstructions of oceanic 13C from sediment cores provide key insights into past as changes in these three drivers. As a step toward full inclusion of 13C in the next generation of Earth system models, we implemented 13C- cycling in a 1° lateral resolution ocean-ice-biogeochemistry Geophysical Fluid Dynamics Laboratory (GFDL) model driven by Common Ocean Reference Experiment perpetual year forcing. The model improved the mean of modern δ13C DIC over coarser resolution GFDL-model implementations, capturing the Southern Ocean decline in surface δ13C DIC that propagates to the deep sea via deep water formation. The model is used here to quantify controls on modern and anthropogenic δ13C DIC as well as to test their sensitivity to wind speed/gas exchange parameterizations. We found that reducing the coefficient for air-sea gas exchange following OMIP-CMIP6 protocols reduces deep sea modern δ13C DIC by 0.2 permil and improves the depth-integrated anthropogenic δ13C DIC relative to previous gas exchange parameterizations. This is because the δ13C DIC of the endmembers ventilating the deep sea and intermediate waters are highly sensitive to the wind speed dependence of the air-sea CO2 gas exchange. Additionally, meridional gradients of surface modern δ13C DIC are better resolved with OMIP-CMIP6. While this model was initially constructed to study the anthropogenic 13C response, it has promising applications toward longer time scales. For example, BLING 13 C includes controls on the biological C-pump thought to be important in the glacial ocean: light and iron limitation, and controls on 13C of organic matter formation, and thus on ocean δ13C DIC and its vertical gradient, that depend on pCO2 .

Detailed descriptions of microbial communities have lagged far behind physical and chemical measurements in the marine environment. Here, we present 971 globally distributed surface ocean metagenomes collected at high spatio-temporal resolution. Our low-cost metagenomic sequencing protocol produced 3.65 terabases of data, where the median number of base pairs per sample was 3.41 billion. The median distance between sampling stations was 26 km. The metagenomic libraries described here were collected as a part of a biological initiative for the Global Ocean Ship-based Hydrographic Investigations Program, or “Bio-GO-SHIP.” One of the primary aims of GO-SHIP is to produce high spatial and vertical resolution measurements of key state variables to directly quantify climate change impacts on ocean environments. By similarly collecting marine metagenomes at high spatiotemporal resolution, we expect that this dataset will help answer questions about the link between microbial communities and biogeochemical fluxes in a changing ocean.

We estimate preformed ocean phosphate, nitrate, oxygen, silicate, and alkalinity by combining a reconstruction of ventilation pathways in the ocean interior with estimates of submixed layer properties. These new preformed property estimates are intended to aid biogeochemical cycling studies and validation of modeled preformed property distributions and are available online. Analyses of net property accumulations (observed minus preformed properties) indicate net remineralization ratios in the ocean interior of [1 P]: [14.1 ± 0.6 N]: [−141 ± 12 O 2 ]: [95 ± 25 Si]: [89 ± 9 TA]. These ratios imply that the interior ocean stores 1,300 (±230) PgC through organic matter remineralization and 540 (±60) PgC through carbonate mineral dissolution and that apparent oxygen utilization can overestimate the interior ocean oxygen consumption by ~25%. Further, only 4 (±1%) and 46 (±5%) of the total alkalinity accumulated from carbonate mineral dissolution are found in seawater that is supersaturated with respect to the aragonite and calcite mineral forms of calcium carbonate, respectively. These small excess alkalinity inventories are due to smaller volumes of the supersaturated water masses and shorter ventilation timescales, as carbonate mineral dissolution rates appear nearly independent of depth and saturation state.

The 13 C/ 12 C of dissolved inorganic carbon ( δ 13 C DIC ) carries valuable information on ocean biological C‐cycling, air‐sea CO 2 exchange, and circulation. Paleo‐reconstructions of oceanic 13 C from sediment cores provide key insights into past as changes in these three drivers. As a step toward full inclusion of 13 C in the next generation of Earth system models, we implemented 13 C‐cycling in a 1° lateral resolution ocean‐ice‐biogeochemistry Geophysical Fluid Dynamics Laboratory (GFDL) model driven by Common Ocean Reference Experiment perpetual year forcing. The model improved the mean of modern δ 13 C DIC over coarser resolution GFDL‐model implementations, capturing the Southern Ocean decline in surface δ 13 C DIC that propagates to the deep sea via deep water formation. Controls on δ 13 C DIC of the deep‐sea are quantified using both observations and model output. The biological control is estimated from the relationship between deep‐sea Pacific δ 13 C DIC and phosphate (PO 4 ). The δ 13 C DIC :PO 4 slope from observations is revised to a value of 1.01 ± 0.02‰ ( μ mol kg −1 ) −1 , consistent with a carbon to phosphate ratio of organic matter (C:P org ) of 124 ± 10. Model output yields a lower δ 13 C DIC :PO 4 than observed due to too low C:P org . The ocean circulation impacts deep modern δ 13 C DIC in two ways, via the relative proportion of Southern Ocean and North Atlantic deep water masses, and via the preindustrial δ 13 C DIC of these water mass endmembers. The δ 13 C DIC of the endmembers ventilating the deep sea are shown to be highly sensitive to the wind speed dependence of air‐sea CO 2 gas exchange. Reducing the coefficient for air‐sea gas exchange following OMIP‐CMIP6 protocols improves significantly surface δ 13 C DIC relative to previous gas exchange parameterizations.

======= DESCRIPTION ======= This is the model output supporting our paper A next generation ocean carbon isotope model for climate studies I: Steady state controls on ocean 13C (2021 Global Biogeochemical Cycles). This model output simulates the transient response of ocean carbon biogeochemistry to anthropogenic CO2 and 13CO2 atmospheric emissions with a nominal lateral resolution of 1° and 50 vertical levels. The model uses the NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) MOM5 coupled to the NOAA-GFDL Biogeochemistry with Light Iron Nutrients and Gas (BLING) with 13C-cycling. Atmospheric forcing is prescribed using the repeating annual cycle of the Common Ocean Reference Experiment version 2 normal year forcing dataset (COREv2-NYF). The implementation of 13C-cycling applies isotopic fractionations during air-sea gas exchange, photosynthetic production of organic matter, and formation of calcium carbonate. The sensitivity of dissolved inorganic 13C in the ocean to the CO2 gas exchange rate is explored by repeating the simulation twice, once using the latest OMIP-CMIP6 protocol for the k-U10 parameterization (standard) and once using the previous OCMIP2 protocol (fast-gas-exchange). Files information: ocean_static.nc: Static fields (longitude, latitude, area). 1990-2002.ocean_month.nc: Monthly output between 1990 and 2002 of ocean physical variables (temperature, salinity, averaged mixed layer depth, maximum mixed layer depth). 1990-2002.ocean_bling_trc_month_CMIP6.nc: Monthly output between 1990 and 2002 of biogeochemical variables* for the simulation using the OMIP-CMIP6 air-sea gas exchange protocol. 1970_1989_d13c_org_mldave_CMIP6.nc: Monthly output between 1970 and 1989 of d13C of organic matter averaged over the mixed layer. 1990-2002.ocean_bling_trc_month_OCMIP2.nc: Monthly output between 1990 and 2002 of biogeochemical variables* for the simulation using the OCMIP2 air-sea gas exchange protocol. * Biogeochemical variables are dissolved inorganic carbon, dissolved inorganic carbon-13, oxygen, and dissolved inorganic phosphate. ======= HOW TO CITE ======= This model output can be freely distributed, but please cite it using the following paper: Claret, M., Sonnerup, R. E., & Quay, P. D. (2021). A next generation ocean carbon isotope model for climate studies I: Steady state controls on ocean 13C. Global Biogeochemical Cycles, 35, e2020GB006757. https://doi.org/10.1029/2020GB006757 ======= ACKNOWLEDGEMENTS ======= This work was funded by the National Science Foundation (NSF-OCE 1356756 and NSF-OCE 1829796). We would also like to acknowledge high-performance computing support from Cheyenne (doi:10.5065/D6RX99HX) provided by NCAR's Computational and Information Systems Laboratory, sponsored by the NSF. ======= QUESTIONS AND REQUESTS? ======= Please contact Mariona Claret (mclaret@uw.edu) or Rolf Sonnerup (rolf@uw.edu).

Assessment of the global budget of the greenhouse gas nitrous oxide ( N 2 O) is limited by poor knowledge of the oceanic N 2 O flux to the atmosphere, of which the magnitude, spatial distribution, and temporal variability remain highly uncertain. Here, we reconstruct climatological N 2 O emissions from the ocean by training a supervised learning algorithm with over 158,000 N 2 O measurements from the surface ocean—the largest synthesis to date. The reconstruction captures observed latitudinal gradients and coastal hot spots of N 2 O flux and reveals a vigorous global seasonal cycle. We estimate an annual mean N 2 O flux of 4.2 ± 1.0 Tg N ⋅ y − 1 , 64% of which occurs in the tropics, and 20% in coastal upwelling systems that occupy less than 3% of the ocean area. This N 2 O flux ranges from a low of 3.3 ± 1.3 Tg N ⋅ y − 1 in the boreal spring to a high of 5.5 ± 2.0 Tg N ⋅ y − 1 in the boreal summer. Much of the seasonal variations in global N 2 O emissions can be traced to seasonal upwelling in the tropical ocean and winter mixing in the Southern Ocean. The dominant contribution to seasonality by productive, low-oxygen tropical upwelling systems (>75%) suggests a sensitivity of the global N 2 O flux to El Niño–Southern Oscillation and anthropogenic stratification of the low latitude ocean. This ocean flux estimate is consistent with the range adopted by the Intergovernmental Panel on Climate Change, but reduces its uncertainty by more than fivefold, enabling more precise determination of other terms in the atmospheric N 2 O budget.

We estimate anthropogenic carbon (C anth ) accumulation rates in the Pacific Ocean between 1991 and 2017 from 14 hydrographic sections that have been occupied two to four times over the past few decades, with most sections having been recently measured as part of the Global Ocean Ship‐based Hydrographic Investigations Program. The rate of change of C anth is estimated using a new method that combines the extended multiple linear regression method with improvements to address the challenges of analyzing multiple occupations of sections spaced irregularly in time. The C anth accumulation rate over the top 1,500 m of the Pacific increased from 8.8 (±1.1, 1σ) Pg of carbon per decade between 1995 and 2005 to 11.7 (±1.1) PgC per decade between 2005 and 2015. For the entire Pacific, about half of this decadal increase in the accumulation rate is attributable to the increase in atmospheric CO 2 , while in the South Pacific subtropical gyre this fraction is closer to one fifth. This suggests a substantial enhancement of the accumulation of C anth in the South Pacific by circulation variability and implies that a meaningful portion of the reinvigoration of the global CO 2 sink that occurred between ~2000 and ~2010 could be driven by enhanced ocean C anth uptake and advection into this gyre. Our assessment suggests that the accuracy of C anth accumulation rate reconstructions along survey lines is limited by the accuracy of the full suite of hydrographic data and that a continuation of repeated surveys is a critical component of future carbon cycle monitoring.

The anthropogenic trace gases chlorofluorocarbon (CFC)-12 and sulfur hexafluoride (SF6) were measured during 2013 in the eastern tropical South Pacific Ocean (ETSP) offshore Chile and Peru (12 degrees-22 degrees S, 70 degrees-86 degrees W). Since the WOCE P21 line along similar to 17 degrees S in 1993, the CFC-12 penetration depth increased from similar to 550 m to similar to 800 m. In 2013, CFC-12 had penetrated through the bottom of the oxygen deficient zone (ODZ, where oxygen (O-2) < 4.5 mu mol kg(-1)) at all stations, indicating that a portion of waters in this ODZ are ventilated on timescales < 60 years. Isopycnal trends in pSF(6) and pCFC-12 ages versus AOU indicated oxygen utilization rates of 11.2 +/- 4.7 mu mol kg(-1) yr(-1) just above the ODZ (90-130 m) and 1.0 +/- 0.5 mu mol kg(-1) yr(-1) beneath the ODZ (400-700 m). Isopycnal trends in pSF(6) ages and nutrients implied fixed N-loss rates of 0.6 +/- 0.4 mu mol kg(-1) yr(-1) at the top of the ODZ (similar to 120 m). The pSF(6) and pCFC-12 ages were significantly younger than mean ages estimated from one-dimensional transit time distributions, which were difficult to constrain using the SF6 and CFC-12 tracer combination. Despite the fact that tracer concentrations tend to underestimate mean ages, and thus overestimate nutrient regeneration/consumption rates, N-loss rates were undetectable (< 0.5 mu mol kg(-1) yr(-1)) within the ODZ itself (similar to 175-400 m). When integrated over depth, the oxygen and nitrogen consumption rates determined above and below the ODZ implied total organic carbon (C) remineralization rates on the order of 0.6 +/- 0.1 mol C m(-2) yr(-1). These low C-export rates, and the decadal ventilation timescale of this ODZ, support a body of work suggesting that the ODZ may be sustained by inputs of high-tracer, low-oxygen waters from the adjacent Peru-Chile coastal upwelling system rather than by organic matter oxidation occurring locally.

Antarctic Bottom Water (AABW) is the coldest, densest, most prolific water mass in the global ocean. AABW forms at several distinct regions along the Antarctic coast and feeds into the bottom limb of the meridional overturning circulation, filling most of the global deep ocean. AABW has warmed, freshened, and declined in volume around the globe in recent decades, which has implications for the global heat and sea level rise budgets. Over the past three decades, the use of tracers, especially time-varying tracers such as chlorofluorocarbons, has been essential to our understanding of the formation, circulation, and variability of AABW. Here, we review three decades of temperature, salinity, and tracer data and analysis that have led to our current knowledge of AABW and how the southern component of deep-ocean ventilation is changing with time.

The anthropogenic CO2 accumulation rate for the Pacific Ocean was estimated from the decrease in C-13 of the dissolved inorganic carbon measured on six World Ocean Circulation Experiment cruises during the 1990s and repeated during Climate Variability and Predictability in the 2000s. A mean depth-integrated anthropogenic C-13 change of -8320mdecade(-1) was estimated for the basin by using the multiple linear regression approach. The largest anthropogenic C-13 decreases occurred between 40 degrees S and 60 degrees S, whereas the smallest decreases occurred in the Southern Ocean and subpolar North Pacific. A mean anthropogenic CO2 accumulation rate of 0.410.13molCm(-2)yr(-1) (0.820.26PgCyr(-1)) was determined based on observed C-13 changes and is in agreement with previous observation- and model-based estimates. The mean dissolved inorganic carbon DIC13 inventory change of -178 +/- 43 parts per thousand molm(-2)decade(-1) was primarily the result of air-sea CO2 exchange acting on the measured air-sea C-13 disequilibrium of similar to-1.2 +/- 0.1 parts per thousand. Regional differences between the DIC13 inventory change and air-sea (CO2)-C-13 flux yielded net anthropogenic CO2 uptake rates (independent of pCO(2)) that ranged from similar to 0 to 1molm(-2)yr(-1) and basin-wide mean of 1.2 +/- 1.5PgCyr(-1). High rates of surface ocean DIC increase and C-13 decrease observed in the Drake Passage (53 degrees S-60 degrees S) support above average anthropogenic CO2 accumulation since 2005. Observed C-13 changes in the Pacific Ocean indicate that ocean transport significantly impacted the anthropogenic CO2 distribution and illustrate the utility of C-13 as a tracer to unravel the processes controlling the present and future accumulation of anth ropogenic CO2 in the ocean.

An offline tracer transport model transport is used to simulate chlorofluorocarbon (CFCs), sulfur hexafluoride (SF6), oxygen, ideal age, and model transit time distributions (TTDs) to evaluate how well tracers can be used to constrain both the mean state and variability of oceanic ventilation. Using climatological transports, the two-parameter 1-D inverse Gaussian approximation of the model TTD is found to be an adequate representation of ventilation pathways within the parts of the subtropical gyres with simple ventilation dynamics, but a poor approximation for regions with large gradients in ideal age (i.e., near the base of the thermocline and the continental boundaries). TTDs inferred from CFC-12 and SF6 using a Peclet number-based lookup table approach yield poor representations of the model TTD with a consistent bias toward ventilation being strongly dominated by along-isopycnal diffusion. In a run with variable circulation, ideal age is used to track changes in thermocline ventilation. Variability in both apparent oxygen utilization (AOU) and tracer-inferred TTD mean ages inferred using CFC-12 (assuming fixed Peclet number) and dual tracers (SF6 and CFC-12) are well-correlated to ideal age variability in most of the thermocline. Changes in AOU are correlated with ideal age variability in even more regions compared to the TTD ages both horizontally and vertically down to intermediate depths. Generally, when changes in TTD mean age and AOU agreed in sign, correlations of both with ideal age changes were positive indicating the usefulness of tracers in diagnosing ventilation changes.

Chlorofluorocarbons-11 (CFC-11), CFC-12, and sulfur hexafluoride (SF6) were measured during the December 2007 to February 2008 CLIVAR/Repeat Hydrography (RH) P18 section along ∼103°W in the Southeast Pacific Ocean. Transit-time distributions (TTDs) of 1-D transport that matched all three tracers were consistent with high Peclet number flow ventilating the subtropical mode water and the main subtropical thermocline (30°S–42°S, 200–800 m). In the subtropics, TTDs with predominantly advective transport predicted decadal increases in CFC-12 and CFC-11 consistent with those observed comparing 1994 WOCE with 2007/2008 CLIVAR/RH data, indicating steady ventilation in this region, and consistent with the near-zero changes observed in dissolved oxygen. The mean transport timescales from the tracer-tuned TTDs were used to estimate apparent oxygen utilization rates (OURs) on the order of 8–20 μmol kg−1 yr−1 at ∼200 m depth, attenuating to ∼2 μmol kg−1 yr−1 typically by 500 m depth in this region. Depth-integrated over the thermocline, these OURs implied carbon export rates from the overlying sea surface on the order of ∼1.8 moles C m−2 yr−1 from 30°S to 45°S, 2–2.5 moles C m−2 yr−1 from 45°S to 52°S, and 2.5–3.5 moles C m−2 yr−1 from 52°S to 60°S.