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Journal Articles - UP - MSI

Permanent URI for this collectionhttps://repository.unesco.gov.ph/handle/123456789/50

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Ocean Decade Challenge: search.filters.odc.Challenge 7: Expand the Global Ocean Observing SystemSDG: search.filters.sdg.SDG 13 - Climate action

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    Nitrite regeneration in the oligotrophic Atlantic Ocean
    Clark, Darren R.; Rees, Andrew P.; Ferrera, Charissa M.; Al-Moosawi, Lisa; Somerfield, Paul J.; Harris, Carolyn; Quartly, Graham D.; Goult, Stephen; Tarran, Glen; Lessin, Gennadi (Copernicus GmbH, 2022-03-07)
    The recycling of scarce nutrient resources in the sunlit open ocean is crucial to ecosystem function. Nitrification directs ammonium (NH4+) derived from organic matter decomposition towards the regeneration of nitrate (NO3-), an important resource for photosynthetic primary producers. However, the technical challenge of making nitrification rate measurements in oligotrophic conditions combined with the remote nature of these environments means that data availability, and the understanding that provides, is limited. This study reports nitrite (NO2-) regeneration rate (RNO2 – the first product of nitrification derived from NH4+ oxidation) over a 13 000 km transect within the photic zone of the Atlantic Ocean. These measurements, at relatively high resolution (order 300 km), permit the examination of interactions between RNO2 and environmental conditions that may warrant explicit development in model descriptions. At all locations we report measurable RNO2 with significant variability between and within Atlantic provinces. Statistical analysis indicated significant correlative structure between RNO2 and ecosystem variables, explaining ∼65 % of the data variability. Differences between sampling depths were of the same magnitude as or greater than horizontally resolved differences, identifying distinct biogeochemical niches between depth horizons. The best overall match between RNO2 and environmental variables combined chlorophyll-a concentration, light-phase duration, and silicate concentration (representing a short-term tracer of water column physical instability). On this basis we hypothesize that RNO2 is related to the short-term autotrophic production and heterotrophic decomposition of dissolved organic nitrogen (DON), which regenerates NH4+ and supports NH4+ oxidation. However, this did not explain the observation that RNO2 in the deep euphotic zone was significantly greater in the Southern Hemisphere compared to the Northern Hemisphere. We present the complimentary hypothesis that observations reflect the difference in DON concentration supplied by lateral transport into the gyre interior from the Atlantic's eastern boundary upwelling ecosystems.
    We thank the crew of the AMT19 cruise. MSLA data were obtained and analysed through the NERC Earth Observation Data Acquisition and Analysis Service (NEODAAS), and further data were provided by the European Space Agency's Sea Level CCI. This is contribution number 320 of the AMT program supported by UKRI through the National Capability Long-term Single Centre Science Programme, Climate Linked Atlantic Sector Science program and further from the Natural Environment Research Council funded Microbial Carbon Pump project. We would like to thank Dennis Hansell and two anonymous reviewers for constructive and insightful comments.
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    Natural and anthropogenic climate variability sgnals in a 237-year-long coral record from the Philippines
    Inoue, Mayuri; Fukushima, A.; Chihara, M.; Genda, A.; Ikehara, Minoru; Okai, T.; Kawahata, Hodaka; Siringan, F. P.; Suzuki, Atsushi (American Geophysical Union, 2023-11-29)
    Both proxy and model studies conducted to understand anthropogenic warming have revealed historical variations in sea-surface temperature (SST) since the industrial revolution. However, because of discrepancies between observations and models in the late nineteenth century, the timing and degree of anthropogenic warming remain unclear. In this study, we reconstructed a 237-year-long record of SST and salinity using a coral core collected from Bicol, southern Luzon, Philippines, which is located at the northern edge of the western Pacific warm pool. The SST record showed volcanic cooling after several volcanic eruptions, including the 1815 Tambora eruption, but the pattern of change differed. Decadal SST variations at Bicol are connected to Pacific Decadal Variability (PDV). Therefore, it is suggested that the PDV conditions at the time of the eruption may have influenced marine conditions, such as the degree and duration of cooling and/or salinity, after the eruptions. Although there were discrepancies in SST variations among the modeled, observed, and proxy SST data from the late nineteenth to early twentieth centuries, SST data from the late twentieth century showed globally coherent anthropogenic warming, especially after 1976. In particular, summer SST in the northwestern Pacific has become more sensitive to anthropogenic forcing since 1976.