The 2010 Deepwater Horizon oil spill resulted in 1.6–2.6 × 1010 grams of petrocarbon accumulation on the seafloor. Data from a deep sediment trap, deployed 7.4 km SW of the well between August 2010 ...and October 2011, disclose that the sinking of spill-associated substances, mediated by marine particles, especially phytoplankton, continued at least 5 mo following the capping of the well. In August/September 2010, an exceptionally large diatom bloom sedimentation event coincided with elevated sinking rates of oil-derived hydrocarbons, black carbon, and two key components of drilling mud, barium and olefins. Barium remained in the water column for months and even entered pelagic food webs. Both saturated and polycyclic aromatic hydrocarbon source indicators corroborate a predominant contribution of crude oil to the sinking hydrocarbons. Cosedimentation with diatoms accumulated contaminants that were dispersed in the water column and transported them downward, where they were concentrated into the upper centimeters of the seafloor, potentially leading to sustained impact on benthic ecosystems.
The marine diatom Thalassiosira pseudonana was grown in continuous culture systems to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO
...(pCO
) on its growth and physiological characteristics. The cells were able to grow at all combinations of low and high irradiance (50 and 300 μmol photons · m
· s
, respectively, of visible light), low and high pCO
(400 and 1,000 μatm, respectively), nutrient limitation (nitrate-limited and nutrient-replete conditions), and temperatures of 10-32°C. Under nutrient-replete conditions, there was no adverse effect of high pCO
on growth rates at temperatures of 10-25°C. The response of the cells to high pCO
was similar at low and high irradiance. At supraoptimal temperatures of 30°C or higher, high pCO
depressed growth rates at both low and high irradiance. Under nitrate-limited conditions, cells were grown at 38 ± 2.4% of their nutrient-saturated rates at the same temperature, irradiance, and pCO
. Dark respiration rates consistently removed a higher percentage of production under nitrate-limited versus nutrient-replete conditions. The percentages of production lost to dark respiration were positively correlated with temperature under nitrate-limited conditions, but there was no analogous correlation under nutrient-replete conditions. The results suggest that warmer temperatures and associated more intense thermal stratification of ocean surface waters could lower net photosynthetic rates if the stratification leads to a reduction in the relative growth rates of marine phytoplankton, and at truly supraoptimal temperatures there would likely be a synergistic interaction between the stresses from temperature and high pCO
(lower pH).
Periodic blooms of salps (pelagic tunicates) can result in high export of organic matter, leading to an “outsized” role in the ocean's biological carbon pump (BCP). However, due to their episodic and ...patchy nature, salp blooms often go undetected and are rarely included in measurements or models of the BCP. We quantified salp‐mediated export processes in the northeast subarctic Pacific Ocean in summer of 2018 during a bloom of Salpa aspera. Salps migrated from 300 to 750 m during the day into the upper 100 m at night. Salp fecal pellet production comprised up to 82% of the particulate organic carbon (POC) produced as fecal pellets by the entire epipelagic zooplankton community. Rapid sinking velocities of salp pellets (400–1,200 m d−1) and low microbial respiration rates on pellets (<1% of pellet C respired day−1) led to high salp pellet POC export from the euphotic zone‐up to 48% of total sinking POC across the 100 m depth horizon. Salp active transport of carbon by diel vertical migration and carbon export from sinking salp carcasses was usually <10% of the total sinking POC flux. Salp‐mediated export markedly increased BCP efficiency, increasing by 1.5‐fold the proportion of net primary production exported as POC across the base of the euphotic zone and by 2.6‐fold the proportion of this POC flux persisting 100 m below the euphotic zone. Salps have unique and important effects on ocean biogeochemistry and, especially in low flux settings, can dramatically increase BCP efficiency and thus carbon sequestration.
Key Points
High salp abundances combined with unique features of salp ecology and physiology lead to their outsized role in the biological pump
During a summer salp bloom in the northeast Pacific Ocean, salp‐mediated carbon export increased the amount and efficiency of carbon export
Salps, especially in otherwise low flux settings, can increase carbon sequestration in the ocean
A study was undertaken to evaluate the role of exocellular polysaccharides in the flocculation of a marine diatom bloom in a large tank mesocosm. Surface-active organic matter was extracted from 1.0 ...μ-filtered tank water by bubble adsorption each day for 7 days of the experiment. In agreement with past studies, particles (3–51 urn equivalent spherical diameter) were readily formed by bubbling and became concentrated in the foam. At the beginning of the bubbling (0–0.5 h), both particles and surface-active carbohydrates were extracted at high rates; however, these rates dropped off steeply after about 0.5 h of bubbling. The rate of particle formation by bubbling could be modeled fairly well by second order kinetics. The extracted, surface-active material was enriched in deoxysugars and galactose, while the residual material was enriched in glucose. Extracted surface-active carbohydrates reached a maximum of 33% of the total dissolved sugars (< 1.0 μm) by the end of the log growth phase. The concentration of extracted surface-active carbohydrates, when normalized to chlorophyll, was strongly correlated (
r
2 > 0.99) with particle stickiness (alpha). In addition, the concentration of surface-active carbohydrates was well correlated (
2 = 0.91) with the concentration of transparent exopolymer particles (TEP) in the tank, and it was demonstrated that TEP could be copiously formed by bubbling of 1.0 μm-filered seawater. The finding of a highly surface-active, deoxysugar-rich polysaccharide material that can be rapidly (<0.5 h) and selectively extracted by bubble adsorption is significant, as it is apparent that this material played important roles in particle stickiness and TEP formation in the tank, and thus it may, at times, play similar roles in particle aggregation in the sea.
The Gulf of Mexico ecosystem is a hotspot for biological diversity and supports a number of industries, from tourism to fishery production to oil and gas exploration, that serve as the economic ...backbone of Gulf coast states. The Gulf is a natural hydrocarbon basin, rich with stores of oil and gas that lie in reservoirs deep beneath the seafloor. The natural seepage of hydrocarbons across the Gulf system is extensive and, thus, the system׳s biological components experience ephemeral, if not, frequent, hydrocarbon exposure. In contrast to natural seepage, which is diffuse and variable over space and time, the 2010 Macondo oil well blowout, represented an intense, focused hydrocarbon infusion to the Gulf׳s deepwaters. The Macondo blowout drove rapid shifts in microbial populations and activity, revealed unexpected phenomena, such as deepwater hydrocarbon plumes and marine “oil snow” sedimentation, and impacted the Gulf׳s pelagic and benthic ecosystems. Understanding the distribution and fate of Macondo oil was limited to some degree by an insufficient ability to predict the physical movement of water in the Gulf. In other words, the available physical oceanographic models lacked critical components. In the past six years, much has been learned about the physical oceanography of the Gulf, providing transformative knowledge that will improve the ability to predict the movement of water and the hydrocarbons they carry in future blowout scenarios. Similarly, much has been learned about the processing and fate of Macondo hydrocarbons. Here, we provide an overview of the distribution, fate and impacts of Macondo hydrocarbons and offer suggestions for future research to push the field of oil spill response research forward.
Gravitational sinking of particles is a key pathway for the transport of particulate organic carbon (POC) to the deep ocean. Particle size and composition influence particle sinking velocity and thus ...play a critical role in controlling particle flux. Canonically, sinking particles that reach the mesopelagic are expected to be either large or ballasted by minerals. However, the presence of transparent exopolymer particles (TEP), which are positively buoyant, may also influence particle sinking velocity. We investigated the relationship between particle composition and sinking velocity during the Export Processes in the Ocean from RemoTe Sensing (EXPORTS) campaign in the Northeast Pacific Ocean using Marine Snow Catchers. Suspended and sinking particles were sized using FlowCam for particle imaging, and their biogeochemical composition was assessed by measuring the concentration of particulate organic carbon (POC) and nitrogen, particulate inorganic carbon, biogenic and lithogenic silica, and TEP. Sinking fluxes were also calculated. Overall, both suspended and sinking particles were small (<51 μm, diameter) in this late summer, oligotrophic system. Contrary to expectation, the ratio of ballast minerals to POC was higher for suspended particles than sinking particles. Further, suspended particles showed TEP-to-POC ratios three times higher than sinking particles. These ratios suggest that TEP content and not ballast dictated whether particles in this system would sink (low TEP) or remain suspended (high TEP). Fluxes of POC averaged 4.3 ± 2.5 mmol C m−2 d−1 at 50 m (n = 9) and decreased to 3.1 ± 1.1 mmol C m−2 d−1 at 300–500 m (n = 6). These flux estimates were slightly higher than fluxes measured during EXPORTS with drifting sediment traps and Thorium-234. A comparison between these approaches illustrates that small sinking particles were an important component of the POC flux in the mesopelagic of this late summer oligotrophic system.
The North Atlantic spring bloom is one of the largest annual biological events in the ocean, and is characterized by dominance transitions from siliceous (diatoms) to calcareous (coccolithophores) ...algal groups. To study the effects of future global change on these phytoplankton and the biogeochemical cycles they mediate, a shipboard continuous culture experiment (Ecostat) was conducted in June 2005 during this transition period. Four treatments were examined: (1) 12°C and 390 ppm CO₂ (ambient control), (2) 12°C and 690 ppm CO₂ (high pCO₂), (3) 16°C and 390 ppm CO₂ (high temperature), and (4) 16°C and 690 ppm CO₂ (‘greenhouse’). Nutrient availability in all treatments was designed to reproduce the low silicate conditions typical of this late stage of the bloom. Both elevated pCO₂ and temperature resulted in changes in phytoplankton community structure. Increased temperature promoted whole community photosynthesis and particulate organic carbon (POC) production rates per unit chlorophylla. Despite much higher coccolithophore abundance in the greenhouse treatment, particulate inorganic carbon production (calcification) was significantly decreased by the combination of increased pCO₂ and temperature. Our experiments suggest that future trends during the bloom could include greatly reduced export of calcium carbonate relative to POC, thus providing a potential negative feedback to atmospheric CO₂ concentration. Other trends with potential climate feedback effects include decreased community biogenic silica to POC ratios at higher temperature. These shipboard experiments suggest the need to examine whether future pCO₂ and temperature increases on longer decadal timescales will similarly alter the biological and biogeochemical dynamics of the North Atlantic spring bloom.
A laboratory experiment was designed to investigate the effects of ocean acidification three levels) in the presence or absence of the clay mineral illite (five concentrations) on the coagulation of ...organic particles. The formation of aggregates. 1 mm from marine detritus and phytoplankton, and their characteristics and sinking velocity, were monitored during the 48 h experiment. Aggregation of particulate organic carbon POC) was independent of both partial pressure of carbon dioxide (P-CO2) and illite addition, implying that the fraction of POC available for export is not affected by either mineral supply or ocean acidification conditions up to ambient + 52.7 Pa P-CO2 (+ 520 ppm). This was true even though the illite appreciably influenced aggregate size, number, and characteristics, including the percentage of transparent exopolymer particles (TEP) incorporated in aggregates. Carbonate chemistry, in the presence of illite, did affect particle formation by clay, carbon, and TEP at the micrometer scale (allocation between dissolved and particulate pools). Our experiment did not resolve processes on this scale well and it remains to be seen if such shifts in the size spectrum of organic carbon and minerals are relevant for the biological pump. High illite content led to small aggregates with a low average sinking velocity. In the absence of biological changes to particle production or loss, coagulation of POC, which is central to the biological pump, is not influenced by ocean acidification or dust input, but sinking velocity and, hence, flux attenuation of POC are likely to be affected by changes in dust input.
PDF
