ALBERT

Description: We present measurements of p CO 2 , O 2 concentration, biological oxygen saturation (ΔO 2 /Ar) and N 2 saturation (ΔN 2 ) in Southern Ocean surface waters during austral summer, 2010–2011. Phytoplankton biomass varied strongly across distinct hydrographic zones, with high chlorophyll a (Chla) concentrations in regions of frontal mixing and sea-ice melt. p CO 2 and ΔO 2 /Ar exhibited large spatial gradients (range 90 to 450 µatm and −10 to 60%, respectively) and co-varied strongly with Chla. However, the ratio of biological O 2 accumulation to dissolved inorganic carbon (DIC) drawdown was significantly lower than expected from photosynthetic stoichiometry, reflecting the differential time-scales of O 2 and CO 2 air-sea equilibration. We measured significant oceanic CO 2 uptake, with a mean air-sea flux (~ −10 mmol m −2 d −1 ) that significantly exceeded regional climatological values. N 2 was mostly supersaturated in surface waters (mean ΔN 2 of +2.5 %), while physical processes resulted in both supersaturation and undersaturation of mixed layer O 2 (mean ΔO 2phys = 2.1 %). Box model calculations were able to reproduce much of the spatial variability of ΔN 2 and ΔO 2phys along the cruise track, demonstrating significant effects of air-sea exchange processes ( e . g . atmospheric pressure changes and bubble injection) and mixed layer entrainment on surface gas disequilibria. Net community production (NCP) derived from entrainment-corrected surface ΔO 2 /Ar data, ranged from ~ −40 to 〉 300 mmol O 2 m −2 d −1 and showed good coherence with independent NCP estimates based on seasonal mixed layer DIC deficits. Elevated NCP was observed in hydrographic frontal zones and stratified regions of sea-ice melt, reflecting physical controls on surface water light fields and nutrient availability.

Description: Abstract The Benguela Upwelling system (BUS) is the most productive of all eastern boundary upwelling ecosystems and it hosts a well‐developed oxygen minimum zone. As such, the BUS is a potential hotspot for production of N2O, a potent greenhouse gas derived from microbially‐driven decay of sinking organic matter. Yet, the extent at which near‐surface waters emit N2O to the atmosphere in the BUS is highly uncertain. Here we present the first high‐resolution surface measurements of N2O across the northern part of the BUS (nBUS). We found strong gradients with a three‐fold increase in N2O concentrations near the coast as compared with open ocean waters. Our observations show enhanced sea‐to‐air fluxes of N2O (up to 1.67 nmol m−2 s−1) in association with local upwelling cells. Based on our data we suggest that the nBUS can account for 13% of the total coastal upwelling source of N2O to the atmosphere.

Description: Abstract High‐quality seawater total alkalinity (AT) measurements are essential for reliable ocean carbon and acidification observations. Well‐established manual multipoint potentiometric titration methods already fulfill these requirements. The next step in the improvement of these observations is the increase of the spatial and temporal measuring resolution with minimal personnel and instrumental effort. For this, a rapid, automated underway analyzer meeting the same high requirements as the traditional method is necessary. In this study, we carried out a comprehensive characterization of the flow‐through analyzer CONTROS HydroFIA® TA (Kongsberg Maritime Contros GmbH, Kiel, Germany) for automated seawater AT measurements in the laboratory and in field with overall more than 5000 measurements. Under laboratory conditions, the analyzer featured a precision of ± 1.5 μmol kg−1 and an accuracy of ± 1.0 μmol kg−1, combined in an uncertainty of 1.6 – 2.0 μmol kg−1. High precision (± 1.1 μmol kg−1) and accuracy (−0.3 ± 2.8 μmol kg−1), and low uncertainty (2.0 – 2.5 μmol kg−1) were also achieved during field trials of 4 and 6 weeks duration. Although a linear drift appears to be the typical behavior of the system, this can be corrected for by regular reference measurements giving consistent measurement results. Another advantage of regular reference measurements is the early detection of any kind of malfunction due to its direct impact on the measurement performance. Based on the present study, recommendations for automated long‐term deployments are provided in order to gain optimal performance characteristics, aiming at the requirements for AT measurements.

Description: The tropical Atlantic exerts a major influence in climate variability through strong air-sea interactions. Within this region, the eastern side of the equatorial band is characterized by strong seasonality, whereby the most prominent feature is the annual development of the Atlantic Cold Tongue (ACT). This band of low sea surface temperatures (∼22-23°C) is typically associated with upwelling-driven enhancement of surface nutrient concentrations and primary production. Based on a detailed investigation of the distribution and sea-to-air fluxes of N 2 O in the eastern equatorial Atlantic (EEA), we show that the onset and seasonal development of the ACT can be clearly observed in surface N 2 O concentrations, which increase progressively as the cooling in the equatorial region proceeds during spring-summer. We observed a strong influence of the surface currents of the EEA on the N 2 O distribution, which allowed identifying “high” and “low” concentration regimes that were, in turn, spatially delimited by the extent of the warm eastward-flowing North Equatorial Countercurrent and the cold westward-flowing South Equatorial Current. Estimated sea-to-air fluxes of N 2 O from the ACT (mean 5.18±2.59 µmol m −2 d −1 ) suggests that in May-July 2011 this cold-water band doubled the N 2 O efflux to the atmosphere with respect to the adjacent regions, highlighting its relevance for marine tropical emissions of N 2 O. This article is protected by copyright. All rights reserved.

Description: The temporal evolution of the physical and biogeochemical structure of an oxygen-depleted anticyclonic modewater eddy is investigated over a 2-month period using high-resolution glider and ship data. A weakly stratified eddy core (squared buoyancy frequency N2  ∼  0.1  ×  10−4 s−2) at shallow depth is identified with a horizontal extent of about 70 km and bounded by maxima in N2. The upper N2 maximum (3–5  ×  10−4 s−2) coincides with the mixed layer base and the lower N2 maximum (0.4  ×  10−4 s−2) is found at about 200 m depth in the eddy centre. The eddy core shows a constant slope in temperature/salinity (T∕S) characteristic over the 2 months, but an erosion of the core progressively narrows down the T∕S range. The eddy minimal oxygen concentrations decreased by about 5 µmol kg−1 in 2 months, confirming earlier estimates of oxygen consumption rates in these eddies. Separating the mesoscale and perturbation flow components reveals oscillating velocity finestructure ( ∼  0.1 m s−1) underneath the eddy and at its flanks. The velocity finestructure is organized in layers that align with layers in properties (salinity, temperature) but mostly cross through surfaces of constant density. The largest magnitude in velocity finestructure is seen between the surface and 140 m just outside the maximum mesoscale flow but also in a layer underneath the eddy centre, between 250 and 450 m. For both regions a cyclonic rotation of the velocity finestructure with depth suggests the vertical propagation of near-inertial wave (NIW) energy. Modification of the planetary vorticity by anticyclonic (eddy core) and cyclonic (eddy periphery) relative vorticity is most likely impacting the NIW energy propagation. Below the low oxygen core salt-finger type double diffusive layers are found that align with the velocity finestructure. Apparent oxygen utilization (AOU) versus dissolved inorganic nitrate (NO3−) ratios are about twice as high (16) in the eddy core compared to surrounding waters (8.1). A large NO3− deficit of 4 to 6 µmol kg−1 is determined, rendering denitrification an unlikely explanation. Here it is hypothesized that the differences in local recycling of nitrogen and oxygen, as a result of the eddy dynamics, cause the shift in the AOU : NO3− ratio. High NO3− and low oxygen waters are eroded by mixing from the eddy core and entrain into the mixed layer. The nitrogen is reintroduced into the core by gravitational settling of particulate matter out of the euphotic zone. The low oxygen water equilibrates in the mixed layer by air–sea gas exchange and does not participate in the gravitational sinking. Finally we propose a mesoscale–submesoscale interaction concept where wind energy, mediated via NIWs, drives nutrient supply to the euphotic zone and drives extraordinary blooms in anticyclonic mode-water eddies.

Description: There is a need for cost-efficient tools to explore deep ocean ecosystems to collect baseline biological observations on pelagic fauna (zooplankton and nekton) and establish the vertical ecological zonation in the deep sea. The Pelagic In situ Observation System (PELAGIOS) is a 3000 m-rated slowly (0.5 m/s) towed camera system with LED illumination, an integrated oceanographic sensor set (CTD-O2) and telemetry allowing for online data acquisition and video inspection (Low Definition). The High Definition video is stored on the camera and later annotated using the VARS annotation software and related to concomitantly recorded environmental data. The PELAGIOS is particularly suitable for open ocean observations of gelatinous fauna, which is notoriously undersampled by nets and/or destroyed by fixatives. In addition to counts, diversity and distribution data as a function of depth and environmental conditions (T, S, O2), in situ observations of behavior, orientation and species interactions are collected. Here we present an overview of the technical setup of the PELAGIOS as well as example observations and analyses from the eastern tropical North Atlantic. Comparisons to MOCNESS net sampling and data from the Underwater Vision Profiler are provided and discussed.

Description: Oxygen optode measurements on floats and gliders suffer from a slow time response and various sources of drift in the calibration coefficients. Based on two dual-O2 Argo floats, we show how to post-correct for the effect of the optode's time response and give an update on optode in situ drift stability and in-air calibration. Both floats are equipped with an unpumped Aanderaa 4330 optode and a pumped Sea-Bird SBE63 optode. Response times for the pumped SBE63 were derived following Bittig et al. (2014) and the same methods were used to correct the time response bias. Using both optodes on each float, the time response regime of the unpumped Aanderaa optode was characterized more accurately than previously possible. Response times for the pumped SBE63 on profiling floats are in the range of 25–40 s, while they are between 60 and 95 s for the unpumped 4330 optode. Our parameterization can be employed to post-correct the slow optode time response on floats and gliders. After correction, both sensors agree to within 2–3 µmol kg−1 (median difference) in the strongest gradients (120 µmol kg−1 change over 8 min or 20 dbar) and better elsewhere. However, time response correction is only possible if measurement times are known, i.e., provided by the platform as well as transmitted and stored with the data. The O2 in-air measurements show a significant in situ optode drift of −0.40 and −0.27 % yr−1 over the available 2 and 3 years of deployment, respectively. Optode in-air measurements are systematically biased high during midday surfacings compared to dusk, dawn, and nighttime. While preference can be given to nighttime surfacings to avoid this in-air calibration bias, we suggest a parameterization of the daytime effect as a function of the Sun's elevation to be able to use all data and to better constrain the result. Taking all effects into account, calibration factors have an uncertainty of 0.1 %. In addition, in-air calibration factors vary by 0.1–0.2 % when using different reanalysis models as a reference. The overall accuracy that can be achieved following the proposed correction routines is better than 1 µmol kg−1.

Description: Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere – the "global carbon budget" – is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on land-cover change data and bookkeeping models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of our imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the last decade available (2007–2016), EFF was 9.4 ± 0.5 GtC yr−1, ELUC 1.3 ± 0.7 GtC yr−1, GATM 4.7 ± 0.1 GtC yr−1, SOCEAN 2.4 ± 0.5 GtC yr−1, and SLAND 3.0 ± 0.8 GtC yr−1, with a budget imbalance BIM of 0.6 GtC yr−1 indicating overestimated emissions and/or underestimated sinks. For year 2016 alone, the growth in EFF was approximately zero and emissions remained at 9.9 ± 0.5 GtC yr−1. Also for 2016, ELUC was 1.3 ± 0.7 GtC yr−1, GATM was 6.1 ± 0.2 GtC yr−1, SOCEAN was 2.6 ± 0.5 GtC yr−1 and SLAND was 2.7 ± 1.0 GtC yr−1, with a small BIM of −0.3 GtC. GATM continued to be higher in 2016 compared to the past decade (2007–2016), reflecting in part the higher fossil emissions and smaller SLAND for that year consistent with El Niño conditions. The global atmospheric CO2 concentration reached 402.8 ± 0.1 ppm averaged over 2016. For 2017, preliminary data indicate a renewed growth in EFF of +2.0 % (range of 0.8 % to 3.0 %) based on national emissions projections for China, USA, and India, and projections of Gross Domestic Product corrected for recent changes in the carbon intensity of the economy for the rest of the world. For 2017, initial data indicate an increase in atmospheric CO2 concentration of around 5.3 GtC (2.5 ppm), attributed to a combination of increasing emissions and receding El Niño conditions. This living data update documents changes in the methods and data sets used in this new global carbon budget compared with previous publications of this data set (Le Quéré et al., 2016; 2015b; 2015a; 2014; 2013). All results presented here can be downloaded from https://doi.org/10.18160/GCP-2017.