The biological carbon pump is a vital component of the global carbon cycle, particularly through the sinking of particulate organic carbon (POC) into the ocean interior. Particle size distribution (PSD) observations from the Underwater Vision Profiler (UVP) have been widely used to quantify sinking POC fluxes. This approach assumes that the sinking POC flux is a function of the PSD multiplied by a power law relating particle size to sinking rates and carbon content. The coefficients of the power law are quantified by regressing UVP data against sediment trap flux observations. Here, we systematically assess the performance of this approach using a large UVP data set of co-located and coincident sediment trap and thorium-234 flux observations from the North Pacific (50 degrees N, 145 degrees W, August 2018) and the North Atlantic (49 degrees N, 16.5 degrees W, May 2021) sampled during the EXPORTS (EXport Processes in the Ocean from RemoTe Sensing) field campaign, which span both diverse environmental conditions and sinking flux values. Globally, when power law coefficients are evaluated over all sites and depths, the UVP flux method explains 80% of the variance in POC flux. However, when coefficients are determined using regional subsets of the EXPORTS data set, the method performs poorly. Reasons include lack of knowledge of particle characteristics beyond PSD, undersampling of rare large particles, spatial and temporal scale mismatches between UVPs and flux observations, and difficulties arising from non-steady state conditions. To improve UVP-based sinking POC flux estimates regionally, additional data on particle characteristics such as transparency and morphology are needed.

The ocean's biological pump, a critical component of the Earth's carbon cycle, transports organic matter from the surface ocean to depth and is dominated by sinking particles, often in the form of marine snow-sized (diameter >= 0.5 mm) aggregates. Controls of sinking particle carbon export are thought to be driven largely using ecological processes that create and transform sinking particles. We diagnose the importance of both biotic and abiotic processes in the dynamics of marine snow and other suspended particles using image-based determination of their size distribution. These observations were made during the demise of the North Atlantic spring bloom in May 2021 as part of the Export Processes in the Ocean from RemoTe Sensing-North Atlantic (EXPORTS-NA) field campaign. We show that intense storm events generated high turbulent mixing rates in the upper ocean that impacted the abundance, size distribution, porosity and sinking of marine snow. Mixed-layer turbulence levels both created and destroyed marine snow and the sequence of entrainment and detrainment of the mixed layer induced by repeated storm forcings enhanced the vertical transport of aggregates to depth. Evidence of biological transformations was also observed at mesopelagic depths, both for the consumption of particulate matter and in the creation of smaller particles from larger ones, likely due to interactions with zooplankton. Collectively, these results illustrate the complex interplay of physical and biological processes regulating the dynamics of marine snow and suggest their inclusion in predictive models of the ocean's biological pump.

The ocean's biological pump, a critical component of the Earth's carbon cycle, transports organic matter from the surface ocean to depth, which is dominated by the sinking particles, often in the form of large (>1 mm) marine snow aggregates. Controls on carbon export are thought to be driven solely by ecological processes that produce and repackage sinking particles. Here, we present observations illustrating the important roles that storm-generated turbulence has on the abundance, characteristics and sinking fluxes of sinking particles. Turbulence creates and destroys aggregates and the vertical mixing induced by storms enhances their vertical transport. Evidence of the importance of biological processes is also observed. In all, these observations illustrate the complex interplay of physical and biological processes regulating the ocean's biological pump and the challenges in creating a predictive understanding of its function.

This manuscript presents an overview of NASA’s EXport Processes in the Ocean from Remote Sensing 2021 Field Campaign in the North Atlantic (EXPORTS NA) and provides quantitative and dynamical descriptions of the physical processes modulating water transformations during the study. A major programmatic goal was to conduct the sampling in a Lagrangian mode so that ocean ecological and biogeochemical changes can be observed independent from physical advective processes. To accomplish this goal, EXPORTS NA conducted a multi-ship, multi-asset field sampling program within a retentive, anticyclonic mode water eddy. Beneath depths of ~100 m, Lagrangian sampling assets remained within the eddy core waters (ECWs) throughout the experiment, demonstrating that the ECWs within the mode water eddy were retentive. However, strong westerly winds from four storm events deepened the mixed layer (ML) of the surface core waters (SCWs) above the eddy’s mode water core by 25-40 m and exchanged some of the SCWs with surface waters outside of the eddy via Ekman transport. Estimates of flushing times ranged from 5-8 days, with surface exchange fractions ranging from 20-75% and were consistent with particle tracking advected by combined geostrophic and Ekman velocities. The relative contributions of horizontal and vertical advection on changes in SCW tracers depend on the horizontal and vertical gradients of that tracer. For example, in the surface waters, horizontal advection played a large role in salinity fluxes, yet vertical entrainment played a larger role in the fluxes of nutrients into the ML. Each storm injected nutrients and low oxygen waters into the ML, after which the surface ocean ecosystem responded by reducing nutrient concentrations and increasing %O2 saturation levels. Overall, SCW values of chlorophyll and POC were the largest at the onset of the field program and decreased throughout the campaign. The analysis presented provides a physical oceanographic context for the many measurements made during the EXPORTS NA field campaign. Illustrated are the many challenges of conducting a production-flux experiment even in a Lagrangian frame and the inherent uncertainties of interpreting biological carbon pump observations that were collected in a Eulerian frame of reference.

The biological carbon pump plays a crucial role in the global carbon cycle, particularly through sinking particles carrying carbon to deep waters. The Underwater Vision Profilers (UVP) is widely used for studying particle properties. UVP-based particulate organic carbon (POC) flux is typically derived from particle size distributions (PSDs) assuming size dependent sinking rates and carbon content. This approach, the “classic UVP method”, calibrates PSD-based flux against sediment trap flux data that are not necessarily co-located in space or time. We put forth a “modified UVP method” that combines a large data set of UVP measurements calibrated against POC flux from co-located and simultaneously collected sediment traps and thorium-234 measurements. Data were collected in the North Pacific (50°N, 145°W, August 2018) and the North Atlantic (49°N, 16.5°W, May 2021) as part of EXPORTS (EXport Processes in the Ocean from RemoTe Sensing), covering a wide range of environmental conditions. We find that our modified UVP methods explain 80% of the variance in POC flux when applied across sites, where flux values vary over orders of magnitude. However, the method fails to account for smaller flux variations within a single site or across depths. Reasons include undersampling rare large particles, mismatch in time and spatial scales of UVPs calibrated against fluxes in traps and 234Th, and difficulties in interpreting particle stock and flux changes within non-steady state conditions. To use UVP as a high-resolution POC flux tool, it is recommended not to rely on a few profiles for calibration.

Mesoscale eddies are a dominant source of spatial variability in the surface ocean and play a major role in the biological marine carbon cycle. Satellite altimetry is often used to locate and track eddies, but this approach is rarely validated against in situ observations. Here we compare measurements of a small (under 25 km radius) mode water anticyclonic eddy over the Procupine Abyssal Plain using CTD and ADCP measurements from 3 ships, 2 gliders, 2 profiling floats, and one Lagrangian float with those derived from sea level anomaly. In situ estimates of the eddy center were estimated from maps of the thickness of its central isopycnal layer, from ADCP velocities at a reference layer, and from the trajectory of the Lagrangian float. These were compared to three methods using altimetric SLA: one based on maximizing geostrophic rotation, one based on a constant SLA contour, and one which maximizes geostrophic velocity speed along the eddy boundary. All algorithms were used to select CTD profiles that were within the eddy. The in-situ metrics agreed to 97\%. The altimetry metrics showed only a small loss of accuracy, giving $>90$\% agreement with the in situ results. This suggests that current satellite altimetry is adequate for understanding the spatial representation of even relatively small mesoscale eddies.

The EXPORTS North Atlantic field campaign (EXPORTS-NA) of May 2021 used a diverse array of ship-based and autonomous platforms to measure and quantify processes leading to carbon export in the open ocean. The success of this field program relied heavily on the ability to make measurements following a Lagrangian trajectory within a coherent, retentive eddy (Sections 1, 2). Identifying an eddy that would remain coherent and retentive over the course of a monthlong deployment was a significant challenge that the EXPORTS team faced. This report details the processes and procedures used by the primarily shore-based eddy tracking team to locate, track, and sample with autonomous assets such an eddy before and during EXPORTS-NA.

The goal of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign is to develop a predictive understanding of the export, fate, and carbon cycle impacts of global ocean net primary production. To accomplish this goal, observations of export flux pathways, plankton community composition, food web processes, and optical, physical, and biogeochemical (BGC) properties are needed over a range of ecosystem states. Here we introduce the first EXPORTS field deployment to Ocean Station Papa in the Northeast Pacific Ocean during summer of 2018, providing context for other papers in this special collection. The experiment was conducted with two ships: a Process Ship, focused on ecological rates, BGC fluxes, temporal changes in food web, and BGC and optical properties, that followed an instrumented Lagrangian float; and a Survey Ship that sampled BGC and optical properties in spatial patterns around the Process Ship. An array of autonomous underwater assets provided measurements over a range of spatial and temporal scales, and partnering programs and remote sensing observations provided additional observational context. The oceanographic setting was typical of late-summer conditions at Ocean Station Papa: a shallow mixed layer, strong vertical and weak horizontal gradients in hydrographic properties, sluggish sub-inertial currents, elevated macronutrient concentrations and low phytoplankton abundances. Although nutrient concentrations were consistent with previous observations, mixed layer chlorophyll was lower than typically observed, resulting in a deeper euphotic zone. Analyses of surface layer temperature and salinity found three distinct surface water types, allowing for diagnosis of whether observed changes were spatial or temporal. The 2018 EXPORTS field deployment is among the most comprehensive biological pump studies ever conducted. A second deployment to the North Atlantic Ocean occurred in spring 2021, which will be followed by focused work on data synthesis and modeling using the entire EXPORTS data set.

This study examines an unprecedented bloom of Emiliania huxleyi along the California coast during the NE Pacific warm anomaly of 2014-2015. Observations of coccolithophore populations from microscopy and flow cytometry, surface current data derived from high-frequency radar, and satellite ocean color imagery were used to track the population dynamics of the bloom in the Santa Barbara Channel. Results show a coastal bloom of mostly E. huxleyi that reached cell concentrations up to 5.7 x 10(6) cells per liter and a maximum spatial extent of 1,220 km(2). We speculate that the rare cooccurrence of warm water, high water column stability, and an extensive preceding diatom bloom during the anomaly contributed to the development of this bloom. Flow cytometry measurements provided insight on the phases of bloom development (e.g., growth versus senescence) with calcified cells comprising up to 64% of particles containing chlorophyll a and detached-coccolith:cell ratios ranging from 10 to >100. Lagrangian particle trajectories estimated during two nonoverlapping 48- and 72-hr periods showed the changes in the surface structure of the bloom due to advection by surface currents and nonconservative biological and physical processes. Time rates of change of particulate inorganic carbon were estimated along particle trajectories, with rates ranging from -4 to 6 molL(-1)day(-1). The approach presented here is likely to be useful for understanding the evolution of coastal phytoplankton bloom events in a general setting. Plain Language Summary This study examines an unprecedented bloom of the coccolithophore Emiliania huxleyi, a single-celled algae that is covered by calcium carbonate plates, along the California coast during a period of unusually warm water during 2014-2015. We used microscopy and flow cytometry, surface current data, and satellite ocean color imagery to track how the bloom changed through time in the Santa Barbara Channel. Results show a coastal bloom of mostly E. huxleyi that reached cell concentrations up to 5.7 x 10(6) cells per liter and covered up to 1,220 km(2). We speculate that the rare cooccurrence of environmental conditions, including warm water, high water column stability, and an extensive preceding diatom bloom during the anomaly, contributed to the development of this bloom. Flow cytometry measurements provided insight on the phases of bloom development (e.g., growth versus senescence) and hourly surface current data to simulate how currents may have moved the coccolithophores during the course of the bloom. In addition, we combined this data with satellite imagery to estimate how the amount of calcium carbonate in this bloom changed through time. The approach presented here is likely to be useful for understanding the rise and fall of phytoplankton blooms along the coast.

Satellite observations of chlorophyll in coastal waters are often described in terms of changes in productivity in response to regional upwelling processes while optical backscattering coefficients are more often linked to episodic inputs of suspended sediments from storm runoff. Here we show that the surface gravity wave resuspension of sediments has a larger role in controlling backscatter than previously considered. Almost 18 years of SeaWiFS, MODIS, MERIS, and VIIRS satellite imagery of the Santa Barbara Channel, California and its surrounding waters spectrally merged with the Garver-Siegel-Maritorena bio-optical model were used to assess the controls on suspended particle distributions. Analysis revealed that chlorophyll blooms in the warmer portions of the domain occur in phase with SST minima, usually in early spring, while blooms in the cooler regions lag SST minima and occur simultaneously to the strongest equatorward winds every year, often in the summer. Tight coupling between the optical variables was seen in offshore areas, as expected for productive waters. However, values of backscatter near the coast were primarily modulated by surface waves. This relationship holds throughout all seasons and is stronger within the 100 m isobath, but often extends tens of kilometers offshore. This forcing of particle resuspension by surface waves is likely a feature ubiquitous in all coastal oceans characterized by fine sediments. The implication of surface wave processes determining suspended particle loads far beyond the surf zone has large consequences for the interpretation of satellite ocean color signals in coastal waters and potentially redefines the extent of the littoral zone.

Absorption of ultraviolet radiation (UV, 280–400nm) by chromophoric dissolved organic matter (CDOM) precedes a host of light-sensitized surface ocean processes relevant to global climate. These include photo- and biogeochemical cycling of organic material, release of sulfur and carbon-containing gases to the atmosphere, and the photoprotection of marine microorganisms. Synoptic CDOM absorption data in the UV is highly desired yet difficult to estimate by satellite methods as the atmosphere interferes with direct detection of water-leaving UV radiance. The absorption spectrum of CDOM is typically modeled as an exponential function in which a spectral slope parameter, S, describes the rate of decrease in absorption with increase in wavelength. Significant functional relationships are observed in aquatic environments between S and the CDOM absorption coefficient at 443nm, aCDOM(443). In this paper, we use a large, systematic dataset of spectroscopic CDOM measurements from the U.S. CO2/CLIVAR Repeat Hydrography Survey to examine the relationship between S and aCDOM(443) as a means to model aCDOM(λ) in the UV from ocean color. Our resultant model predicts aCDOM(λ) at wavelengths from 325 to 412nm from the absorption coefficient of colored dissolved and detrital materials (CDM) at 443nm, aCDM(443), retrieved by an existing semi-analytical ocean color algorithm. Expected agreement (near 1:1) with the training dataset was achieved (r2=0.71–0.85, p=0, n=127). Considering inherent satellite data uncertainties as well as the model's limitations in regions with potential terrestrial influence, good correspondence between modeled and in situ values was observed during independent validation with open ocean CDOM data, such as from BIOSOPE (r2=0.77–0.85, p<0.05, n=29). The model has immediate application in global scale assessments of photochemical rate processes and CDOM cycling in the open ocean due to its simplicity and optimization using a large base of field data (>7500 samples) from diverse Case I waters.

Large-scale climate patterns influenced temperature and weather patterns around the globe in 2011. In particular, a moderate-to-strong La Nina at the beginning of the year dissipated during boreal spring but reemerged during fall. The phenomenon contributed to historical droughts in East Africa, the southern United States, and northern Mexico, as well the wettest two-year period (2010-11) on record for Australia, particularly remarkable as this follows a decade-long dry period. Precipitation patterns in South America were also influenced by La Nina. Heavy rain in Rio de Janeiro in January triggered the country's worst floods and landslides in Brazil's history.The 2011 combined average temperature across global land and ocean surfaces was the coolest since 2008, but was also among the 15 warmest years on record and above the 1981-2010 average. The global sea surface temperature cooled by 0.1 degrees C from 2010 to 2011, associated with cooling influences of La Nina. Global integrals of upper ocean heat content for 2011 were higher than for all prior years, demonstrating the Earth's dominant role of the oceans in the Earth's energy budget. In the upper atmosphere, tropical stratospheric temperatures were anomalously warm, while polar temperatures were anomalously cold. This led to large springtime stratospheric ozone reductions in polar latitudes in both hemispheres. Ozone concentrations in the Arctic stratosphere during March were the lowest for that period since satellite records began in 1979. An extensive, deep, and persistent ozone hole over the Antarctic in September indicates that the recovery to pre-1980 conditions is proceeding very slowly.Atmospheric carbon dioxide concentrations increased by 2.10 ppm in 2011, and exceeded 390 ppm for the first time since instrumental records began. Other greenhouse gases also continued to rise in concentration and the combined effect now represents a 30% increase in radiative forcing over a 1990 baseline. Most ozone depleting substances continued to fall. The global net ocean carbon dioxide uptake for the 2010 transition period from El Nino to La Nina, the most recent period for which analyzed data are available, was estimated to be 1.30 Pg C yr(-1), almost 12% below the 29-year long-term average.Relative to the long-term trend, global sea level dropped noticeably in mid-2010 and reached a local minimum in 2011. The drop has been linked to the La Nina conditions that prevailed throughout much of 2010-11. Global sea level increased sharply during the second half of 2011.Global tropical cyclone activity during 2011 was well-below average, with a total of 74 storms compared with the 1981-2010 average of 89. Similar to 2010, the North Atlantic was the only basin that experienced above-normal activity. For the first year since the widespread introduction of the Dvorak intensity-estimation method in the 1980s, only three tropical cyclones reached Category 5 intensity level-all in the Northwest Pacific basin.The Arctic continued to warm at about twice the rate compared with lower latitudes. Below-normal summer snowfall, a decreasing trend in surface albedo, and above-average surface and upper air temperatures resulted in a continued pattern of extreme surface melting, and net snow and ice loss on the Greenland ice sheet. Warmer-than-normal temperatures over the Eurasian Arctic in spring resulted in a new record-low June snow cover extent and spring snow cover duration in this region. In the Canadian Arctic, the mass loss from glaciers and ice caps was the greatest since GRACE measurements began in 2002, continuing a negative trend that began in 1987. New record high temperatures occurred at 20 m below the land surface at all permafrost observatories on the North Slope of Alaska, where measurements began in the late 1970s. Arctic sea ice extent in September 2011 was the second-lowest on record, while the extent of old ice (four and five years) reached a new record minimum that was just 19% of normal.On the opposite pole, austral winter and spring temperatures were more than 3 degrees C above normal over much of the Antarctic continent. However, winter temperatures were below normal in the northern Antarctic Peninsula, which continued the downward trend there during the last 15 years. In summer, an all-time record high temperature of -12.3 degrees C was set at the South Pole station on 25 December, exceeding the previous record by more than a full degree. Antarctic sea ice extent anomalies increased steadily through much of the year, from briefly setting a record low in April, to well above average in December. The latter trend reflects the dispersive effects of low pressure on sea ice and the generally cool conditions around the Antarctic perimeter.

Phytoplankton photosynthesis in the sun lit upper layer of the global ocean is the overwhelmingly dominant source of organic matter that fuels marine ecosystems. Phytoplankton contribute roughly half of the global (land and ocean) net primary production (NPP; gross photosynthesis minus plant respiration) and phytoplankton carbon fixation is the primary conduit through which atmospheric CO2 concentrations interact with the ocean s carbon cycle. Phytoplankton productivity depends on the availability of sunlight, macronutrients (e.g., nitrogen, phosphorous), and micronutrients (e.g., iron), and thus is sensitive to climate-driven changes in the delivery of these resources to the euphotic zone

Satellite altimetry and hydrographic observations are used to characterize the mesoscale eddy field in the Sargasso Sea near Bermuda and to address the role of physical processes on the supply of new nutrients to the euphotic zone. The observed sea level anomaly (SLA) field is dominated by the occurrence of westward propagating features with SLA signatures as large as 25 cm, Eulerian temporal scales of roughly a month, lifetimes of several months, spatial scales of ∼200 km, and a propagation of ∼5 cm s −1 . Hydrographic estimates of dynamic height anomaly (referenced to 4000 dbar) are well correlated with satellite SLA ( r 2 = 0.65), and at least 85% of the observed dynamic height variability is associated with the first baroclinic mode of motion. This allows us to apply the satellite observations to remotely estimate isopycnal displacements and the flux of nutrients into the euphotic zone due to eddy pumping. Eddy pumping is the process by which mesoscale eddies induce isopycnal displacements that lift nutrient‐replete waters into the euphotic zone, driving new primary production. A kinematic approach to the estimation of the eddy pumping results in a flux of 0.24 ± 0.1 mol N m −2 yr −1 (including a scale estimate for the small contribution due to 18° water eddies). This flux is more than an order of magnitude larger than the diapycnal diffusive flux as well as scale estimates for the vertical transport due to isopycnal mixing along sloping isopycnal surfaces. Eddy pumping and wintertime convection are the two dominant mechanisms transporting new nutrients into the euphotic zone, and the sum of all physical new nutrient supply fluxes effectively balances previous geochemical estimates of annual new production for this site. However, if biological transports (e.g., nitrogen fixation, etc.) are significant, the new nitrogen supply budget will be in excess of geochemical new production estimates. This suggests that the various physical and biological transport fluxes, as well as geochemical inferences of new production, still need to be reconciled and many outstanding questions remain.

Recent optical, physical, and biological oceanographic observations are used to assess the magnitude and variability of the penetrating flux of solar radiation through the mixed layer of the warm water pool (WWP) of the western equatorial Pacific Ocean. Typical values for the penetrative solar flux at the climatological mean mixed layer depth for the WWP (30 m) are ∼23 W m−2 and are a large fraction of the climatological mean net air‐sea heat flux (∼40 W m−2). The penetrating solar flux can vary significantly on synoptic timescales. Following a sustained westerly wind burst, in situ solar fluxes were reduced in response to a near tripling of mixed layer phytoplankton pigment concentrations. This results in a reduction in the penetrative flux at depth (5.6 W m−2 at 30 m) and corresponds to a biogeochemically mediated increase in the mixed layer radiant heating rate of 0.13°C per month. These observations demonstrate a significant role of biogeochemical processes on WWP thermal climate. We speculate that this biogeochemically mediated feedback process may play an important role in enhancing the rate at which the WWP climate system returns to normal conditions following a westerly wind burst event.

: A new method of calibrating Inverted Echo Sounder (IES) travel time measurements to main thermocline depths is described. Unlike the traditional method in which the thermocline is defined by a point measurement, such as the depth of the 12 deg C isotherm depth as measured with an XBT, this technique utilizes the full temperature profile of XBT casts. The advantage of this method is that the vertical integral of temperature, QT= Tdz is conceptually and empirically very closely correlated with the acoustic travel time measured by the IES, r=2 c-1 dz. Comparisons of the new method with the more traditional point method show that the root-mean-square error in the calibration (11 m standard deviation) is 1/3 as large as before, and outlier values are significantly reduced. The final coefficients used to calibrate the SYNOP Central and Inlet Array IESs are tabulated.

: The Inverted Echo Sounder (IES) is an instrument that acoustically monitors the depth of the main thermocline from a moored position one meter above the ocean floor. Additionally, the IESs can be equipped to measure both pressure and temperature. The standard steps for processing IES data are documented here. The effect and purpose of each step are discussed followed by a description of how to apply the computer programs that constitute the step. The FORTRAN and MATLAB codes are also supplied.

: The SYNoptic Ocean Prediction experiment (SYNOP) was undertaken with the goal that increased understanding of the Gulf Stream obtained through coordinated observations could be integrated with numerical models, including predictive models of the Gulf Stream. Our moored experiment, which began in fall of 1987, consists of two separate arrays in the Gulf Stream as part of the SYNOP program. The 'Inlet array of inverted echo sounders (IES) and deep current meters measure key parameters that describe the variability of the Gulf Stream and deep western boundary current (DWBC) near Cape Hatteras. In this region the Gulf Stream first flows into deeper water and crosses over the DWBC. The 'Central' array of IESs, in a 350 km square centered on the Gulf Stream near 68 W, monitors the thermocline structure of the Gulf Stream in the region of large meanders and frequent interactions with rings. The array also contains twelve tall current meter moorings that reach into the Gulf Stream core. Most of the IESs in the interior of the array are outfitted with bottom pressure recorders. This report documents IES data recovered during the summer of 1989 by plots and tables of basic statistics and pertinent deployment information. The plots are time series of measured travel time, pressure, temperature; the residual pressure; and low-pass filtered records of residual pressure, thermocline depth, and temperature.