NOAA Atlantic Oceanographic and Meteorological Laboratories

Ocean warming threatens the persistence of tropical corals and the biologically diverse ecosystems they sustain. While field-based studies on heat impact have predominantly focused on quantifying coral bleaching, a symptom of thermal stress, less attention has been given to understanding trends in coral mortality, a critical metric for assessing and predicting the long-term effects of rising temperatures. Consequently, the relationships between varying heat exposures and resultant coral cover changes remain poorly quantified. Such trends are challenging to establish in the Tropical and Subtropical Western Atlantic (TWA), because climate change impacts are compounded by local anthropogenic and natural disturbances. Additionally, many coral communities have already been substantially altered, with those remaining dominated by relatively resilient species. This study addresses this issue by quantifying coral cover loss as a function of maximum Degree Heating Weeks (DHW) exposure using observed in-situ coral cover changes across reefs in the TWA. Of the five locations assessed (the Florida Keys, Dry Tortugas, Puerto Rico, the US Virgin Islands, and the East and West Flower Garden Banks), all exhibited significant declines in mean coral cover with increasing DHW exposure. Rates ranged from 0.3% to 2.4% annual loss in relative mean cover per unit DHW, with spatial variability largely reflecting pre-impact system conditions and variations in the life-history traits of geographically distinct coral assemblages (e.g., Puerto Rico vs East and West Flower Garden Banks). Variation in responses to DHW among species was also observed across locations. By establishing site-specific coral loss parameters, this study contributes to our understanding of how future coral cover may evolve under escalating thermal stress in the TWA. It also provides practical guidance for targeted restoration by identifying species that have fared comparatively well across locations, grounding efforts in what is possible under current and future conditions rather than idealised historical baselines.

Abstract Observation‐based estimates of the Atlantic Meridional Overturning Circulation (AMOC) and meridional heat transport (MHT) are necessary to better understand their evolution in the coming years. The RAPID‐MOCHA‐WBTS array at 26°N is the only trans‐Atlantic observing system to provide 20+ years of continuous measurements of the AMOC and MHT. While the design of the array has continuously evolved as our understanding of the AMOC has advanced, and as new technologies have become available, a new goal is to design a lower‐cost and more sustainable observing system to continue AMOC estimations with high accuracy. Using the RAPID array data and ocean reanalyzes, we evaluate the error in the AMOC estimate due to the choice of data included in its calculation. We find that the trend and variability of the volume transport in the upper 3,000‐m of the water column are not captured with sufficient accuracy by synoptic hydrographic data or ocean reanalyzes. However, moorings in the deep ocean interior along the eastern boundary and the Mid‐Atlantic ridge can be replaced by hydrographic data from repeat trans‐Atlantic hydrographic sections to reliably estimate the AMOC trend and variability. Experiments simulating the observing system in a high‐resolution ocean model further show that the additional error in the long‐term AMOC estimate induced by the substitution of mooring measurements below 3,000‐m depth at these locations is small (0.30 Sv) as compared to the AMOC uncertainty.

Abstract Seasonal North Atlantic tropical cyclone (TC) activity is largely regulated by El Niño–Southern Oscillation (ENSO), Atlantic meridional mode (AMM) and Atlantic multidecadal variability (AMV), and the associated difference in sea surface temperatures (SSTs) between the Atlantic main development region (10°–20°N, 60°–20°W) and the equatorial Pacific. However, the fluctuating amplitudes and phases of ENSO, AMM, and other climate modulators contribute to a spatial inhomogeneity of seasonal hurricane activity throughout the North Atlantic basin, over which TC impacts may vary significantly. For instance, ENSO is known to modulate Atlantic vertical wind shear more acutely in the western tropical North Atlantic, thus influencing TC development in close proximity to the United States. Additionally, Atlantic Niño has recently been shown to enhance the development of powerful TCs in the eastern tropical North Atlantic. Therefore, analysis of subbasin seasonal TC activity would enable the development of “user-oriented” outlooks (e.g., U.S. Gulf Coast energy sector) to better inform regional stakeholder interests. While seasonal outlooks of North Atlantic hurricane activity have been available for decades, skilled predictions of subbasin TC activity have been elusive and are not yet incorporated in official seasonal forecasts. We refine the Pacific–Atlantic interbasin SST relationship to develop seasonal probabilistic outlooks targeting the operational forecast criteria of NOAA’s Seasonal Atlantic Hurricane Outlook (i.e., terciles of below-, near-, and above-normal TC activity) for five specific North Atlantic subbasins (e.g., Caribbean, U.S. Gulf Coast, U.S. East Coast, subtropical North Atlantic, and tropical North Atlantic). We find skill in forecasting seasonal subbasin accumulated cyclone energy for above- and below-normal seasons using SST predictors from the North American Multimodel Ensemble, though strong correlations between the subbasin forecasts limit the predictive usefulness. Overall, there are marginal improvements in forecasting subbasin seasonal TC activity when compared with a “full-basin” forecast, with the Caribbean achieving the most substantial increase in probabilistic forecast skill.

<strong class="journal-contentHeaderColor">Abstract.</strong> The marine biological carbon pump (BCP) plays a central role in the global carbon cycle, transporting carbon from the surface to the deep ocean and sequestering it for long periods. Sinking of surface-produced particles, known as the Biological Gravity Pump (BGP) constitutes the main component of the BCP. To study the BGP in the equatorial Atlantic upwelling region, a biogeochemical (BGC) Argo float equipped with an Underwater Vision Profiler 6 (UVP6) camera was deployed from July 2021 to March 2022. The float was recovered after its eastward drift from 23&deg; W to 7&deg; W along the equator, during which it conducted profiles to 2000 m depth every three days. For the first time in this oceanic region, in situ images and physical and biogeochemical data from a BGC-Argo float were acquired and analyzed in combination with satellite data. During the float trajectory, two blooms were recorded followed by two main export events of sinking aggregates that lasted for over a month, consistently reaching 2000 m depth. A Lagrangian approach was applied to investigate the production, transformation, and deep export of marine particles. Based on the characterization of the morphology of detritus within and outside of the plumes, five particle morphotypes with different sinking properties were detected. Small and dense aggregates were present throughout the water column while porous morphotypes, despite being larger, were predominantly concentrated in the surface layer. Export was driven by small and compact particles with higher particle abundance and flux during upwelling and export events. Our investigation reveals the stability of the equatorial Atlantic BCP system during this period, yielding an export efficiency of 6&ndash;7 % during and outside of export events. This study highlights the importance of using new technologies on autonomous platforms to characterize the temporal variability in the magnitude and functioning of the BCP.

The Southern Ocean plays a key role in removing anthropogenic carbon dioxide (CO2) from the atmosphere, accounting for a quarter of the global ocean uptake during the Anthropocene period. Here we show, using a high-resolution ocean model under high-emission forcing (RCP8.5), that the Southern Ocean contribution to the global ocean CO2 sink increases from 40 to 50% by 2100. This increase is accompanied by a robust poleward shift in the ocean CO2 sink. Specifically, regions north and south of the maximum zonal wind stress (located between 50-55°S) exhibit distinct carbon-uptake trajectories. The southern region (poleward of 55°S) exhibits a near-linear increase in annual carbon uptake, from near 0 to 0.75 Pg C yr-1 over the century. In contrast, the northern region (35-50°S) carbon uptake increases over the 1st half of the century, from 0.8 to 1.2 Pg C yr-1, but stagnates afterward. Our analysis indicates that the former is due to the high turnover rate (upwelling followed by subduction) of the Circumpolar Deep Water, which becomes increasingly undersaturated relative to atmospheric CO2, while the latter is due to weakening carbon solubility after the mid-21st century. Finally, the resolution in this study allows for the representation of mesoscale eddies. Eddy activity is generally enhanced along with the poleward shift in the zonal wind forcing, but its net impact on the air-sea exchange of carbon appears to be minimal.

The convective boundary layer height (CBLH) is a crucial variable that needs to be parameterized within the planetary boundary layer (PBL) scheme in models; however, significant discrepancies persist between model-derived and instrument-observed CBLH

Long-term reanalysis data from the Bluelink ReANalysis 2020 are used to investigate temperature variability from 2010 to 2020 in the Jailolo Strait–Halmahera Sea, which is part of the Indonesian Throughflow (ITF) eastern route. The analysis shows that net surface heat flux (NSHF) mainly affects semiannual mixed layer temperature (MLT) variability. Vertical turbulent mixing cools the mixed layer from below, while the vertical and horizontal advection have less impact on the MLT heat budget. In the upper thermocline (40-100 m), two temperature minima occur: one in April due to outflow to the Pacific Ocean, and another in August due to uplifted water. Different cooling processes mark the dominant annual variation in the mid thermocline (100-150 m depth) and the lower thermocline (150-200 m). The cooling process is mainly associated with the transport from the Pacific Ocean into the Indonesian Seas (inflow) in the mid-thermocline, while it is generally related to the outflow transport in the lower thermocline. Interannual temperature variation is marked by the relatively colder (warmer) sea surface temperature and shallowing (deepening) thermocline during the El Niño (La Niña) period, which is associated with the upwelling (downwelling) Rossby wave propagation. It is also found that the colder (warmer) temperature in the upper 200 m during the El Niño (La Niña) period correlates with the weaker (stronger) inflow from the Pacific Ocean into the Indonesian Seas. • The BRAN2020 dataset is used to study temperature variability in the Jailolo Strait • Net surface heat flux primarily drives semiannual mixed layer temperature variability • Vertical turbulent mixing cools the mixed layer from the thermocline • Rossby waves from the Pacific Ocean appear to propagate in the Jailolo Strait

The El Nin&amp;#771;o-Southern Oscillation (ENSO) strongly influences phytoplankton in the tropical Pacific, with El Nin&amp;#771;o conditions suppressing productivity in the equatorial Pacific (EP) and placing nutritional stresses on marine ecosystems. The Geophysical Fluid Dynamics Laboratory's (GFDL) Earth System Model version 4.1 (ESM4.1) captures observed ENSO-chlorophyll patterns (r = 0.57) much better than GFDL's previous ESM2M (r = 0.23). Most notably, the observed post-El Nin&amp;#771;o &amp;#8220;chlorophyll rebound&amp;#8221; is substantially improved in ESM4.1 (r = 0.52). We find that an anomalous increase in iron propagation from western Pacific (WP) subsurface to the cold tongue via the equatorial undercurrent (EUC) and subsequent post-El Nin&amp;#771;o surfacing, unresolved in ESM2M, is the primary driver of chlorophyll rebound. We also find that this chlorophyll rebound is augmented by high post-El Nin&amp;#771;o dust-iron deposition anomalies in the eastern EP. This post-El Nin&amp;#771;o chlorophyll rebound provides a previously unrecognized source of marine ecosystem resilience independent from the La Nin&amp;#771;a that sometimes follows.

Abstract. The marine biological carbon pump (BCP) plays a central role in the global carbon cycle, transporting carbon from the surface to the deep ocean and sequestering it for long periods. Sinking of surface-produced particles, known as the Biological Gravity Pump (BGP) constitutes the main component of the BCP. To study the BGP in the equatorial Atlantic upwelling region, a biogeochemical (BGC) Argo float equipped with an Underwater Vision Profiler 6 (UVP6) camera was deployed from July 2021 to March 2022. The float was recovered after its eastward drift from 23° W to 7° W along the equator, during which it conducted profiles to 2000 m depth every three days. For the first time in this oceanic region, in situ images and physical and biogeochemical data from a BGC-Argo float were acquired and analyzed in combination with satellite data. During the float trajectory, two blooms were recorded followed by two main export events of sinking aggregates that lasted for over a month, consistently reaching 2000 m depth. A Lagrangian approach was applied to investigate the production, transformation, and deep export of marine particles. Based on the characterization of the morphology of detritus within and outside of the plumes, five particle morphotypes with different sinking properties were detected. Small and dense aggregates were present throughout the water column while porous morphotypes, despite being larger, were predominantly concentrated in the surface layer. Export was driven by small and compact particles with higher particle abundance and flux during upwelling and export events. Our investigation reveals the stability of the equatorial Atlantic BCP system during this period, yielding an export efficiency of 6–7 % during and outside of export events. This study highlights the importance of using new technologies on autonomous platforms to characterize the temporal variability in the magnitude and functioning of the BCP.

Tropical cyclones models have long used nesting to achieve higher resolution of the inner core than was feasible for entire model domains. These high resolution nests have been shown to better capture storm structures and improve forecast accuracy. The Hurricane Analysis and Forecast System (HAFS) is the new-generation numerical model embedded within NOAA’s Unified Forecast System (UFS). The document highlights the importance of high horizontal resolution (2 km or finer) in accurately simulating the small-scale features of tropical cyclones, such as the eyewall and eye. To meet this need, HAFS was developed by NOAA leveraging a high-resolution, storm-following nest. This nest moves with the cyclone, allowing better representation of small-scale features and more accurate feedback between the cyclone’s inner core and the larger environment. This hurricane following nest capability, implemented in the Finite-Volume Cubed-Sphere (FV3) dynamical core within the UFS framework, can be run both within the regional as well as global forecast systems. A regional version of HAFS with a single moving nest went into operations in 2023. HAFS also includes the first ever moving nest implemented within a global model which is currently being used for research. In this document we provide details of the implementation of moving nests and provide some of the results from both global and regional simulations. For the first time NOAA P3 flight data was used to evaluate the inner core structure from the global run.