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In order to calculate net community production (NCP) rates on Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) transect cruises, gas tracer data were collected with a continuous at-sea mass spectrometer. The ratio of O2/Ar, measured continuously from underway water, yields 8,000-15,000 rates of NCP per cruise. Discrete water samples (50 to 150 per cruise) were collected for triple oxygen isotope (TOI) analysis to estimate gross primary production (GPP) rates and ratios of NCP/GPP. Along-shelf (upstream-downstream) transects were conducted in addition to the main across-shelf transect. This data package provides two types of data tables for NES-LTER transect cruises beginning in 2018: a high-frequency continuous Equilibration Inlet Mass Spectrometer (EIMS) table, provided by year, and a low-frequency discrete triple oxygen isotope (TOI) table with all years combined. Rates calculated from these measurements are provided as separate packages, per year, in the EDI repository. 

This data package provides net community production (NCP) and gross oxygen production (GOP, a measure of gross primary production) for the winter, spring, and summer Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises in 2019. Two tables are provided: a high-frequency table with NCP rates calculated from measurements of O2/Ar made continuously by an at-sea equilibrator inlet mass spectrometer (EIMS), and a low-frequency table with both NCP and GOP rates calculated for discrete samples measured post-cruise. The GOP rates were calculated from triple O2 isotopic (TOI) ratios. These data are derived from the EIMS and TOI data for the NES-LTER Transect cruises in EDI data package knb-lter-nes.6.2. 

This data package provides net community production (NCP) and gross oxygen production (GOP, a measure of gross primary production) for the winter, summer, and fall Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) Transect cruises in 2018. Two tables are provided: a high-frequency table with NCP rates calculated from measurements of O2/Ar made continuously by an at-sea equilibrator inlet mass spectrometer (EIMS), and a low-frequency table with both NCP and GOP rates calculated for discrete samples measured post-cruise. The GOP rates were calculated from triple O2 isotopic (TOI) ratios. These data are derived from the EIMS and TOI data for the NES-LTER Transect cruises in EDI data package knb-lter-nes.6.2. 

Gas exchange between the atmosphere and ocean interior profoundly impacts global climate and biogeochemistry. However, our understanding of the relevant physical processes remains limited by a scarcity of direct observations. Dissolved noble gases in the deep ocean are powerful tracers of physical air-sea interaction due to their chemical and biological inertness, yet their isotope ratios have remained underexplored. Here, we present high-precision noble gas isotope and elemental ratios from the deep North Atlantic (~32°N, 64°W) to evaluate gas exchange parameterizations using an ocean circulation model. The unprecedented precision of these data reveal deep-ocean undersaturation of heavy noble gases and isotopes resulting from cooling-driven air-to-sea gas transport associated with deep convection in the northern high latitudes. Our data also imply an underappreciated and large role for bubble-mediated gas exchange in the global air-sea transfer of sparingly soluble gases, including O 2 , N 2 , and SF 6 . Using noble gases to validate the physical representation of air-sea gas exchange in a model also provides a unique opportunity to distinguish physical from biogeochemical signals. As a case study, we compare dissolved N 2 /Ar measurements in the deep North Atlantic to physics-only model predictions, revealing excess N 2 from benthic denitrification in older deep waters (below 2.9 km). These data indicate that the rate of fixed N removal in the deep Northeastern Atlantic is at least three times higher than the global deep-ocean mean, suggesting tight coupling with organic carbon export and raising potential future implications for the marine N cycle. 

Abstract The Mid‐Atlantic Bight (MAB) hosts a large and productive marine ecosystem supported by high phytoplankton concentrations. Enhanced surface chlorophyll concentrations at the MAB shelf‐break front have been detected in synoptic measurements, yet this feature is not present in seasonal means. To understand why, we assess the conditions associated with enhanced surface chlorophyll at the shelf break. We employ in‐situ and remote sensing data, and a 2‐dimensional model to show that Ekman restratification driven by upfront winds drives ephemerally enhanced chlorophyll concentrations at the shelf‐break front in spring. Using 8‐day composite satellite‐measured surface chlorophyll concentration data from 2003–2020, we constructed a daily running mean (DRM) climatology of the cross‐shelf chlorophyll distribution for the northern MAB region. While the frontal enhancement of chlorophyll is apparent in the DRM climatology, it is not captured in the seasonal climatology due to its short duration of less than a week. In‐situ measurements of the frontal chlorophyll enhancement reveal that chlorophyll is highest in spring when the shelf‐break front slumps offshore from its steep wintertime position causing restratification in the upper part of the water column. Several restratification mechanisms are possible, but the first day of enhanced chlorophyll at the shelf break corresponds to increasing upfront winds, suggesting that the frontal restratification is driven by offshore Ekman transport of the shelf water over the denser slope water. The 2‐dimensional model shows that upfront winds can indeed drive Ekman restratification and alleviate light limitation of phytoplankton growth at the shelf‐break front. 

Abstract Climatic changes have decreased the stability of the Gulf Stream (GS), increasing the frequency at which its meanders interact with the Mid‐Atlantic Bight (MAB) continental shelf and slope region. These intrusions are thought to suppress biological productivity by transporting low‐nutrient water to the otherwise productive shelf edge region. Here we present evidence of widespread, anomalously intense subsurface diatom hotspots in the MAB slope sea that likely resulted from a GS intrusion in July 2019. The hotspots (at ∼50 m) were associated with water mass properties characteristic of GS water (∼100 m); it is probable that the hotspots resulted from the upwelling of GS water during its transport into the slope sea, likely by a GS meander directly intruding onto the continental slope east of where the hotspots were observed. Further work is required to unravel how increasingly frequent direct GS intrusions could influence MAB marine ecosystems.