Decolonising Environmental Risk Assessments of Potentially Polluting Wrecks:a Case Study of the Wreck of the USS Mississinewa in Ulithi Lagoon, Federated States of Micronesia

Millions of tonnes of oil lie entombed within wrecks from two world wars which, when released, can cause environmental devastation. Wrecks are predominantly risk assessed by the Global North Nations responsible, resulting in an epistemology that separates human from nature. This research aimed to decolonise risk assessments to capture the spatially heterogeneous nature of human vulnerability to oil pollution. Triangulation analysis of interviews and official reports relating to the USS Mississinewa oil spill identified three Global South issues a Eurocentric risk assessment failed to capture: region-specific meteorological conditions causing the leak, remoteness making external resources slow to arrive, and the impact of the fishery closure on traditional subsistence lifestyles. A vulnerability assessment is proposed to prioritise wrecks in susceptible locations. Recommendations are made for a collaborative approach to wreck management by including local voices, resisting the Global North assumption of generality, and recognising the priorities of those living with wrecks

Bacterioplankton dynamics in surface waters of the north-eastern (sub-)tropical Atlantic Ocean affected by Aeolian dust

The microbial community dominates biogeochemical cycling of the ocean, affecting global climate.The impact of physical disturbance of near surface microbial populations was studied in the northeasterntropical and subtropical Atlantic Ocean. This region lies beneath easterly trade winds,resulting in strong perturbations in terms of wind driven mixing and Aeolian dust deposition.Firstly, the region’s surface water bacterioplankton community was compared with adjacentregions in terms of metabolic activity, by measuring the uptake rates of radioactively labelledamino acids (3H-leucine and 35S-methionine) as a proxy for bacterial production. Remarkably, therewas little variation in uptake rates between the two Atlantic (sub-)tropical gyres. Rates reflectedregional photosynthetic biomass, except in the study region. The bacterioplankton community ofthis region was less metabolically active than that of the oligotrophic north Atlantic gyre, despiteocean colour data identifying the region as productive. The region’s uniqueness is probably relatedto the episodic Saharan dust inputs experienced.To test whether dust deposition controls microbial community structure, surface communitieswere compared, using flow cytometry and fluorescence in situ hybridisation, between two winterperiods when either wind-driven mixing or dust deposition occurred. Wind-driven mixing wasassociated with domination by the ubiquitous SAR11 clade of Alphaproteobacteria, whereas keyprimary producers, Prochlorococcus cyanobacteria, numerically dominated during calmerconditions. Phytoplankton-associated Bacteroidetes and Synechococcus cyanobacteria were mostabundant during turbulent conditions. Gammaproteobacteria, encompassing opportunistic species,were the only group to benefit from dust inputs; thus dust deposition seems to have a minorinfluence on the region’s bacterioplankton community compared to wind mixing, suggestingcommunity change following dust storm events may be linked to nutrients delivered by windmixing, as much as from dust.To test further whether changes in the SAR11 and Prochlorococcus populations varied betweenyears due to wind- or dust-related perturbation, a method based on 35S-methionine uptake wasdeveloped for measuring the metabolic response of these groups to Aeolian dust, whilst excludingwind impacts. Subsurface seawater samples were treated with freshly collected dust, addeddirectly or indirectly as a “leachate” after its rapid dissolution in deionised water. Prochlorococcusand SAR11 cells were sorted by flow cytometry to determine their group-specific responses. BothProchlorococcus and SAR11 were metabolically impaired by the addition of dust, which may explainthe low metabolic activity observed in the region (mentioned above). Although SAR11 showedminor positive responses to dust leachate additions, leachate proved detrimental to Prochlorococcus.Thus dust dissolution in situ appears to be more deleterious to Prochlorococcus than SAR11 andhence could initiate a compositional shift in the indigenous bacterioplankton, suggesting theobserved switch from SAR11- to Prochlorococcus-domination following dust deposition (mentionedabove) was indeed a result of an alternative stimulus, most likely wind stress.In conclusion, whereas dust deposition may prove beneficial to bacterioplankton species withhigh nutrient demands, such as some Gammaproteobacteria, it does not appear to affect the ambientdominant bacterioplankton groups of the northeast (sub-)tropical Atlantic to the same degree aswind-driven perturbations. Furthermore, large dust deposition events may prove detrimental toambient populations, resulting in low community metabolic activity