Search for: All records

The West Florida Shelf (WFS) is oligotrophic, with inorganic N and P concentrations typically at or below detection limits, and yet significant rates of primary productivity, including blooms of the cyanobacterial diazotroph Trichodesmium spp. as well as the harmful algal species Karenia brevis, are observed there. Consequently, dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) are thought to be the primary sources of assimilative nutrients on the WFS. Here we report measurements of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrations made on samples collected on a cruise in July of 2023 aboard the R/V Endeavor. Elevated concentrations of TDN (>12 µM) and TDP (>0.5 µM) were observed in the shallow, nearshore region, while to the west concentrations of both TDN and TDP decreased to values typically associated with oligotrophic North Atlantic waters (4 to 5 µM TDN and 0.05 to 0.1 µM TDP). 

The West Florida Shelf (WFS) is oligotrophic, with inorganic N and P concentrations typically at or below detection limits, and yet significant rates of primary productivity, including blooms of the cyanobacterial diazotroph Trichodesmium spp. as well as the harmful algal species Karenia brevis, are observed there. Consequently, dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) are thought to be the primary sources of assimilative nutrients on the WFS. Here we report measurements of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrations made on samples collected quarterly from rivers draining onto the WFS as well as from submarine groundwater wells on three transects extending from the Florida Nature Coast in the north to Venice Headland in the south. Elevated concentrations of TDN (>12 µM) and TDP (>0.5 µM) were observed in riverine and groundwater samples, as well as in the shallow, nearshore region, while to the west concentrations of both TDN and TDP decreased to values typically associated with oligotrophic North Atlantic waters (4 to 5 µM TDN and 0.05 to 0.1 µM TDP). 

The West Florida Shelf (WFS) is oligotrophic, with inorganic N and P concentrations typically at or below detection limits, and yet significant rates of primary productivity, including blooms of the cyanobacterial diazotroph Trichodesmium spp. as well as the harmful algal species Karenia brevis, are observed there. Consequently, dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) are thought to be the primary sources of assimilative nutrients on the WFS. Here we report measurements of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrations made on samples collected on a cross-shelf cruise in Feb-Mar 2023 aboard the R/V Atlantic Explorer. Elevated concentrations of TDN (>12 µM) and TDP (>0.5 µM) were observed in the shallow, nearshore region, while to the west concentrations of both TDN and TDP decreased to values typically associated with oligotrophic North Atlantic waters (4 to 5 µM TDN and 0.05 to 0.1 µM TDP). 

Specific activities of long-lived dissolved radium (Ra-226, Ra-228), collected from U.S. Geological Survey small boat operations in the West Florida Shelf from November 2022 to March 2024. Small boat samples include surface water, bottom water, and submarine groundwaters from three well transects along Nature Coast, Indian Rocks Beach, and Venice Headlands. This project investigates how boundary sources, including rivers and submarine groundwater discharge, deliver important nutrients and metals to the coastal ecosystems of the West Florida Shelf. Here, dissolved radium isotopes have been measured to trace boundary sources of nutrients and metals entering the West Florida Shelf. 

In 2021, a collaborative scientific investigation (National Science Foundation Grant Award OCE-2148989, Project 880516) was started for the purpose of quantifying shelf inventories and boundary fluxes of dissolved organic nitrogen and dissolved iron to the West Florida Shelf (WFS) to assess their role in supporting the oligotrophic WFS ecosystem. To assess the spatial and temporal variability in submarine groundwater as a boundary source to the shelf, scientists from the U.S. Geological Survey (USGS), St. Petersburg Coastal and Marine Science Center (SPCMSC) designed a marine well network (three transects of wells across different coastal regions) and conducted five sampling events over a 16-month period. For each trip, samples were collected from shallow (< 10 meters [m] water depth) offshore groundwater wells and coincidental water column stations. Samples were collected from the different water types for the determination of naturally occurring, short-lived isotopes of radium (Ra): Ra-223 (half-life, t1/2 = 11.4 days) and Ra-224 (t1/2 = 3.63 days). Identifiers for the transects and subsequent samples are two to three letter acronyms based on coastal communities or geographic features in Florida: Nature Coast near Hudson (NC); Indian Rocks Beach near Indian Rocks Beach (IRB), and Venice Headland near Venice (VH). Radium-223 and Radium-224 were absorbed onto manganese (di)oxide impregnated fibers (referred to as Mn-fibers from hereon) following exposure to seawater and the fiber was retained as the sample. The activities of Radium-223 and Radium-224 absorbed onto the Mn-fibers were measured on a set of Radium Delayed Coincidence Counters (RaDeCC) as outlined originally in Moore and Arnold (1996) and updated for procedural recommendations by Diego-Feliu and others (2020). Data included in this data release correspond to USGS Field Activity Number (FAN) 2022-340-FA, with associated events spanning over one year (November 2022 to March 2024) and are distinguished by alternative field activity numbers (Alt FANs) of 22WFS05, 23WFS01, 23WFS02, 23WFS03, 23WFS04, 24WFS01. Samples were acquired in November 2022, January-February 2023, May-June 2023, September 2023, December 2023, and February-March 2024, respectively. Moore, W.S., and Arnold, R., 1996, Measurement of 223Ra and 224Ra in coastal waters using a delayed coincidence counter: Journal of Geophysical Research, v. 101, no. C1, p. 1321-1329, https://doi.org/10.1029/95JC03139. Note: This data release was versioned on August 13, 2025. Please see the Suggested Citation section for details. 

This dataset includes the specific activities of dissolved radon-222 collected from grab samples during STING I cruise AE2305 on R/V Atlantic Explorer (February to March 2023) and STING II cruise EN704 on R/V Endeavor in the Gulf of Mexico (June to July 2023). Additional data collected from underway samples during STING II are provided in the related dataset. This project investigates how boundary sources, including rivers and submarine groundwater discharge, deliver important nutrients and metals to the coastal ecosystems of the West Florida Shelf. Here, dissolved radon-222 has been measured to trace boundary sources of nutrients and metals entering the West Florida Shelf, including submarine groundwater discharge. 

Activities of dissolved radium (Ra-223, Ra-224, Ra-226, Ra-228), Th-228, and Ac-227, collected on two cruises in the Gulf of Mexico. STING I cruise AE2305 on R/V Atlantic Explorer was deployed from February to March 2023. STING II consisted of EN704 on R/V Endeavor and U.S. Geological Survey small boat surveys and took place from June to July 2023. This project investigates how boundary sources, including rivers and submarine groundwater discharge, deliver important nutrients and metals to the coastal ecosystems of the West Florida Shelf. Here, dissolved radium and parent isotopes have been measured to trace boundary sources of nutrients and metals entering the West Florida Shelf. 

The West Florida Shelf (WFS) in the Gulf of America (formerly the Gulf of Mexico) is oligotrophic, with inorganic nitrogen (N) and phosphorus (P) concentrations typically at or below detection limits, and yet significant rates of primary productivity, including blooms of the harmful algal species Karenia brevis, are observed there. Additionally, multiple clades of the cyanobacterial diazotroph Trichodesmium spp. are endemic on the WFS. Consequently, dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) are thought to be the primary sources of assimilative macro nutrients on the WFS. Here we present results from a multidisciplinary study conducted on spring and summer 2023 cruises that 1) quantified rates of N2 fixation on the WFS; 2) characterized the diazotroph community composition; 3) measured dissolved inorganic and organic and suspended particulate organic nutrient concentrations and isotopic compositions; 4) measured trace element concentrations, speciation, and isotopic composition; 5) characterized dissolved organic matter chemical composition; and, 6) quantified fluxes of these elements from submarine groundwater discharge using a radium isotope mass balance model. Additionally, quarterly sampling of the geochemistry of riverine and submarine groundwater wells defined the chemical composition of margin (i.e., riverine and submarine groundwater) inputs. Together, we use these results to understand whether submarine groundwater discharge is the dominant source of bioavailable DON, DOP, dissolved iron, and iron-binding ligands on the WFS. Additionally, we use the results to ask whether the abundance of Karenia brevis and Trichodesmium spp. are associated with enhanced submarine groundwater inputs, and whether rates of N2 fixation carried out by two different Trichodesmium spp. are associated with enhanced submarine groundwater inputs. 

Because nitrogen availability limits primary production over much of the global ocean, understanding the controls on the marine nitrogen inventory and supply to the surface ocean is essential for understanding biological productivity and exchange of greenhouse gases with the atmosphere. Quantifying the ocean’s inputs, outputs, and internal cycling of nitrogen requires a variety of tools and approaches, including measurements of the nitrogen isotope ratio in organic and inorganic nitrogen species. The marine nitrogen cycle, which shapes nitrogen availability and speciation in the ocean, is linked to the elemental cycles of carbon, phosphorus, and trace elements. For example, the majority of nitrogen cycle oxidation and reduction reactions are mediated by enzymes that require trace metals for catalysis. Recent observations made through global-scale programs such as GEOTRACES have greatly expanded our knowledge of the marine nitrogen cycle. Though much work remains to be done, here we outline key advances in understanding the marine nitrogen cycle that have been achieved through these analyses, such as the distributions and rates of dinitrogen fixation, terrestrial nitrogen inputs, and nitrogen loss processes. 

Surface ocean marine dissolved organic matter (DOM) serves as an important reservoir of carbon (C), nitrogen (N), and phosphorus (P) in the global ocean, and is produced and consumed by both autotrophic and heterotrophic communities. While prior work has described distributions of dissolved organic carbon (DOC) and nitrogen (DON) concentrations, our understanding of DOC:DON:DOP stoichiometry in the global surface ocean has been limited by the availability of DOP concentration measurements. Here, we estimate mean surface ocean bulk and semi‐labile DOC:DON:DOP stoichiometry in biogeochemically and geographically defined regions using newly available marine DOM concentration databases. Global mean surface ocean bulk (C:N:P = 387:26:1) and semi‐labile (C:N:P = 179:20:1) DOM stoichiometries are higher than Redfield stoichiometry, with semi‐labile DOM stoichiometry similar to that of global mean surface ocean particulate organic matter (C:N:P = 160:21:1) reported in a recent compilation. DOM stoichiometry varies across ocean basins, ranging from 251:17:1 to 638:43:1 for bulk and 83:15:1 to 414:49:1 for semi‐labile DOM C:N:P, respectively. Surface ocean DOP concentration exhibits larger relative changes than DOC and DON, driving surface ocean gradients in DOC:DON:DOP stoichiometry. Inferred autotrophic consumption of DOP helps explain intra‐ and inter‐basin patterns of marine DOM C:N:P stoichiometry, with regional patterns of water column denitrification and iron supply influencing the biogeochemical conditions favoring DOP use as an organic nutrient. Specifically, surface ocean marine DOM exhibits increasingly P‐depleted stoichiometries from east to west in the Pacific and from south to north in the Atlantic, consistent with patterns of increasing P stress and alleviated iron stress.