Phosphorous cycling in the Gulf of Maine : a multi-tracer approach

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1998Knowledge of temporal and spatial nutrient turnover and export rates is of great importance for a variety of investigations, ranging from nutrient limitation to contamination uptake and removal. However, there are few methods that allow for the in situ elucidation of these processes. In this thesis research, in situ phosphorus turnover rates and upper ocean export were determined within the southwestern Gulf of Maine using the naturally occurring radionuclides phosphorus-32 (t_= 14.3 d), phosphorus-33 (t_ = 25.3 d), thorium-234 (t_ = 24.1) and beryllium-7 (t_ = 53.3 d). New techniques were developed for the extraction, purification and measurement of 32p and 33p in rainwater and in inorganic, organic and particulate pools in seawater. In order to constrain the input ratio of 33p/32p, rain samples were collected and measured continuously for 32p and 33p, as well as 7Be and 21OPb, from March 1996 to March 1998 at Woods Hole, MA, and from March 1997 to October 1997 at Portsmouth, NH. The average 33p;32p ratio was 0.88 ± 0.14. 32p, 33p, 7Be and 210Pb were further used to determine aerosol residence times and as possible tracers of stratospheric/tropospheric exchange during severe storm events. F our cruises were conducted in Wilkinson Basin, in the Gulf of Maine, during the spring and summer of 1997. 234Th was used to estimate advection and diffusion using 1D steady state and multi-dimensional non-steady state models. Export ratios (export/primary production) were found to range between 0.11 and 0.37. Vertical eddy diffusivity found using 7Be varied from 0.5 to 1.5 cm2 sec-I. Significant changes in phosphorus turnover rates within the reservoirs which contained 32p and 33p activity were found between the spring and summer months. In late summer, bacterial activity was substantial, significantly affecting the residence times of dissolved inorganic and organic phosphorus pools. Our results clearly show that 32p and 33p can provide much needed information regarding the biogeochemical cycling of P in marine systems and can be of use in the development of ecosystem models which seek to address mechanisms which affect primary production in the ocean.Funding for this work was provided by the Office of Naval Research Fellowship Program, The Environmental Protection Agency Science to Achieve Results (STAR) Fellowship Program, the National Science Foundation (Grant no. OCE-9633240) and the Woods Hole Oceanographic Institution (unrestricted funds)

Phosphorus cycling in the Gulf of Maine : a multi-tracer approach

Thesis (Ph.D.)--Joint Program in Oceanography, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 1999 [February 1999]Vita.Includes bibliographical references.by Claudia R. Benitez-Nelson.Ph.D

South Carolina Stormwater Detention Ponds: Sediment Accumulation and Nutrient Sequestration

Stormwater detention ponds are prevalent across South Carolina and receive runoff waters carrying both nutrients and sediments. As sediments accumulate in these ponds, water volume is reduced leading to a decrease in runoff retention. Periodic dredging is required to maintain pond function, but dredging is costly and there is little data available to support how often pond dredging is required. It is further unknown how high nutrient loading effects sediment nutrient sequestration and autochthonous production of organic sediment components

A Time Series of Water Column Distributions and Sinking Particle Flux of Pseudo-Nitzschia and Domoic Acid in the Santa Barbara Basin, California

Water column bulk Pseudo-nitzschia abundance and the dissolved and particulate domoic acid (DA) concentrations were measured in the Santa Barbara Basin (SBB), California from 2009–2013 and compared to bulk Pseudo-nitzschia cell abundance and DA concentrations and fluxes in sediment traps moored at 147 m and 509 m. Pseudo-nitzschia abundance throughout the study period was spatially and temporally heterogeneous (L−1 to 3.8 × 106 cells L−1 , avg. 2 × 105 ± 5 × 105 cells L−1 ) and did not correspond with upwelling conditions or the total DA (tDA) concentration, which was also spatially and temporally diverse (1000 cells L−1 and tDA = 200 ng L−1 ) measured as deep as 150 m. Our results highlight that dDA should not be ignored when examining bloom toxicity. Although water column abundance and pDA concentrations were poorly correlated with sediment trap Pseudo-nitzschia abundance and fluxes, DA toxicity is likely associated with senescent blooms that rapidly sink to the seafloor, adding another potential source of DA to benthic organisms

Insights into Particle Formation and Remineralization Using the Short-Lived Radionuclide, Thorium-234

[1] Simple mass balance models are applied to a high resolution 234Th profile from the northwest Pacific to examine the magnitude, rate, and depth distribution of particle remineralization processes below the euphotic zone (Ez). Here, excess 234Th (234Th \u3e 238U) below the Ez is attributed to fragmentation processes that result in the conversion of sinking to non‐sinking particles. By considering particulate organic carbon (POC) to 234Th ratios on particles, we show that POC flux attenuation is larger than for 234Th, which we attribute to bacterial and zooplankton consumption of sinking POC. Three case studies are used to demonstrate how different combinations of particle fragmentation and POC respiration impact flux attenuation below the Ez. When sampled with high vertical resolution and precision, 234Th and POC/234Th ratios provide insights into both export from the Ez and the extent to which sinking particle fluxes and associated minerals are attenuated with depth

Review of the analysis of 234Th in small volume (2–4 L) seawater samples: Improvements and recommendations

The short-lived radionuclide 234Th is widely used to study particle scavenging and transport from the upper ocean to deeper waters. This manuscript optimizes, reviews and validates the collection, processing and analyses of total 234Th in seawater and suggests areas of further improvements. The standard 234Th protocol method consists of scavenging 234Th from seawater via a MnO2 precipitate, beta counting, and using chemical recoveries determined by adding 230Th. The revised protocol decreases sample volumes to 2 L, shortens wait times between steps, and simplifies the chemical recovery process, expanding the ability to more rapidly and safely apply the 234Th method

Review of the analysis of Th-234 in small volume (2-4 L) seawater samples: improvements and recommendations

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Clevenger, S. J., Benitez-Nelson, C. R., Drysdale, J., Pike, S., Puigcorbe, V., & Buesseler, K. O. Review of the analysis of Th-234 in small volume (2-4 L) seawater samples: improvements and recommendations. Journal of Radioanalytical and Nuclear Chemistry, 329(1), (2021): 1–13, https://doi.org/10.1007/s10967-021-07772-2.The short-lived radionuclide 234Th is widely used to study particle scavenging and transport from the upper ocean to deeper waters. This manuscript optimizes, reviews and validates the collection, processing and analyses of total 234Th in seawater and suggests areas of further improvements. The standard 234Th protocol method consists of scavenging 234Th from seawater via a MnO2 precipitate, beta counting, and using chemical recoveries determined by adding 230Th. The revised protocol decreases sample volumes to 2 L, shortens wait times between steps, and simplifies the chemical recovery process, expanding the ability to more rapidly and safely apply the 234Th method.The authors would like to acknowledge support from the National Aeronautics and Space Administration (NASA) as part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) program awards 80NSSC17K0555; and the Woods Hole Oceanographic Institution’s Ocean Twilight Zone study for KOB and SJC

Potential Role of Inorganic Polyphosphate in the Cycling of Phosphorus Within the Hypoxic Water Column of Effingham Inlet, British Columbia

[1] The upper basin of Effingham Inlet possesses permanently anoxic bottom waters, with a water column redox transition zone typically occurring at least 40 m above the sediment‐water interface. During our sampling campaign in April and July 2007, this redox transition zone was associated with sharp peaks in a variety of parameters, including soluble reactive phosphorus (SRP) and total particulate phosphorus (TPP). Based on sequential extraction results, TPP maxima exhibited preferential accumulation of an operationally defined class of loosely adsorbed organic phosphorus (P), which may contain a substantial fraction of polyphosphate (poly‐P). This poly‐P may furthermore be involved in the redox‐dependent remobilization of SRP. For example, direct fluorometric analysis of poly‐P content revealed that particulate inorganic poly‐P was present at concentrations ranging from 1 to 9 nM P within and several meters above the TPP maximum. Below the depth of 1% oxygen saturation, however, particulate inorganic poly‐P was undetectable

Sea Surface pCO2‐SST Relationships Across a Cold‐Core Cyclonic Eddy: Implications for Understanding Regional Variability and Air‐Sea Gas Exchange

[1] This study is designed to improve the understanding of how biologically productive, cold‐core cyclonic eddies affect sea surface pCO2 in the lee of the main Hawaiian Islands in the subtropical North Pacific Gyre. We identified three unique relationships between pCO2 and sea surface temperature (SST). A positive correlation between pCO2 and SST was observed in the waters surrounding the eddy suggesting surface CO2 is controlled primarily by thermodynamics. In contrast, a negative relationship was observed within the eddy core as a result of the upwelling of CO2‐enriched subsurface waters. A third relationship existed throughout the rest of the eddy with reduced pCO2 suggesting a combination of biological uptake, physical upwelling and thermodynamic controls. In the absence of an eddy, this region is a CO2 sink, with the passage of the cold‐core mesoscale eddy decreasing the magnitude of the sink by ∼17%. However, if the general temperature correlation is used to predict pCO2 inside the cold eddy, it would overestimate the CO2 sink inside the eddy by 100%

Magnitude and Composition of Sinking Particulate Phosphorus Fluxes in Santa Barbara Basin, California

[1] The composition and bioavailability of particulate P influence marine biological community production on both modern and geologic time‐scales, and continental margins play a critical role in the supply, modification, and storage of particulate P. This study examined particulate P cycling in the Santa Barbara Basin (SBB) off the coast of southern California using a ∼520 m deep‐moored sediment trap deployed from 1993–2006 and a sediment core collected in 2005 directly beneath the sediment trap at 590 m. Total particulate P (TPP), particulate inorganic P (PIP), and particulate organic P (POP) were quantified using a 5‐step sequential extraction method (SEDEX) that chemically separates PIP into loosely bound, oxide‐bound, authigenic, and detrital P phases. POP fluxes, while similar in magnitude to other coastal regions (22 ± 10 μmol m−2 d−1) were a small component of the TPP pool (15%). Seasonal trends revealed significant increases in POP fluxes during upwelling due to increased biological production in surface waters by organisms that increased mineral ballast. High particulate organic carbon (POC) to POP ratios (337 ± 18) further indicated rapid and efficient remineralization of POP relative to POC as particles sank through the oxic water column; however, further reduction of POP ceased in the deeper anoxic waters. Loosely bound, oxide‐bound, and authigenic P, dominated the TPP pool, with PIP fluxes substantially higher than those measured in other coastal settings. Strong correlations between oxide‐associated, authigenic, and detrital P fluxes with lithogenic material indicated a terrestrial source associated with riverine discharge. Furthermore, more than 30% of the loosely bound and oxide‐bound P was remineralized prior to burial, with the magnitude of dissolution far exceeding that of POP. These results highlight the dynamic nature of the particulate P pool in coastal ecosystems and how changes in P source can alter the composition and lability of P that enters coastal waters