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Browsing by Author "Thomalla, Sandy J"

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Absence of photophysiological response to iron addition in autumn phytoplankton in the Antarctic sea-ice zone

Author: Singh, Asmita ; Fietz, S ; Thomalla, Sandy J ; Sanchez, N ; Ardelan, MV ; Moreau, S ; Kauko, HM ; Fransson, A ; Chierici, M ; Ryan-Keogh, Thomas J Date: Jul 2023 The high nutrient–low chlorophyll condition of the Southern Ocean is generally thought to be caused by the low bioavailability of micronutrients, particularly iron, which plays an integral role in phytoplankton photosynthesis. Nevertheless, ... Read more
Bacteria and archaea regulate particulate organic matter export in suspended and sinking marine particle fractions

Author: Dithugoe, Choaro D ; Bezuidt, OKI ; Cavan, EL ; Froneman, WP ; Thomalla, Sandy J ; Makhalanyane, TP Date: Apr 2023 The biological carbon pump (BCP) in the Southern Ocean is driven by phytoplankton productivity and is a significant organic matter sink. However, the role of particle-attached (PA) and free-living (FL) prokaryotes (bacteria and archaea) and ... Read more
Calibration of an in-water multi-excitation fluorometer for the measurement of phytoplankton chlorophyll-a fluorescence quantum yield

Author: Griffith, Derek J ; Bone, Emma L ; Thomalla, Sandy J ; Bernard, Stewart Date: Jul 2018 A multi-excitation fluorometer (MFL, JFE Advantech Co., Ltd.), originally designed to discriminate between phytoplankton species present within a population, has been redirected for use in fluorescence quantum yield (FQY) determination. While ... Read more
Deriving a proxy for iron limitation from chlorophyll fluorescence on buoyancy gliders

Author: Ryan-Keogh, Thomas J ; Thomalla, Sandy J Date: May 2020 Chlorophyll fluorescence, primarily used to derive phytoplankton biomass, has long been an underutilized source of information on phytoplankton physiology. Diel fluctuations in chlorophyll fluorescence are affected by both photosynthetic ... Read more
Evaluation of chlorophyll-a and POC MODIS aqua products in the Southern Ocean

Author: Moutier, William ; Thomalla, Sandy J ; Bernard, Stewart ; Wind, G ; Ryan-Keogh, Thomas J ; Smith, Marie E Date: Jul 2019 The Southern Ocean (SO) is highly sensitive to climate change. Therefore, an accurate estimate of phytoplankton biomass is key to being able to predict the climate trajectory of the 21st century. In this study, MODerate resolution Imaging ... Read more
High latitude Southern Ocean phytoplankton have distinctive bio-optical properties

Author: Robinson, CM ; Huot, Y ; Schuback, N ; Ryan-Keogh, Thomas J ; Thomalla, Sandy J ; Antoine, D Date: Jul 2021 Studying the biogeochemistry of the Southern Ocean using remote sensing relies on accurate interpretation of ocean colour through bio-optical and biogeochemical relationships between quantities and properties of interest. During the Antarctic ... Read more
High-resolution view of the spring bloom initiation and net community production in the Subantarctic Southern Ocean using glider data

Author: Thomalla, Sandy J ; Racault, M ; Swart, S ; Monteiro, Pedro MS Date: Jul 2015 In the Southern Ocean, there is increasing evidence that seasonal to subseasonal temporal scales, and meso- to submesoscales play an important role in understanding the sensitivity of ocean primary productivity to climate change. This drives ... Read more
Isotopic evidence for nitrification in the Antarctic winter mixed layer

Author: Smart, SM ; Fawcett, SE ; Thomalla, Sandy J ; Weigand, MA ; Reason, CJC ; Sigman, DM Date: Apr 2015 We report wintertime nitrogen and oxygen isotope ratios (δ15N and δ18O) of seawater nitrate in the Southern Ocean south of Africa. Depth profile and underway surface samples collected in July 2012 extend from the subtropics to just beyond the ... Read more
Multidecadal trend of increasing iron stress in Southern Ocean phytoplankton

Author: Ryan-Keogh, Thomas J ; Thomalla, Sandy J ; Scheel Monteiro, Pedro M ; Tagliabue, A Date: Feb 2023 Southern Ocean primary productivity is principally controlled by adjustments in light and iron limitation, but the spatial and temporal determinants of iron availability, accessibility, and demand are poorly constrained, which hinders accurate ... Read more
Nitrogen uptake by phytoplankton in the Atlantic sector of the Southern Ocean during late austral summer

Author: Joubert, WR ; Thomalla, Sandy J ; Waldron, HN ; Lucas, MI ; Boye, M ; Le Moigne, FAC ; Planchon, F ; Speich, S Date: 2011 As part of the Bonus-GoodHope (BGH) campaign, 15N-labelled nitrate, ammonium and urea uptake measurements were made along the BGH transect from Cape Town to ~60° S in late austral summer, 2008. Our results are categorised according to distinct ... Read more
An optimized method for correcting fluorescence quenching using optical backscattering on autonomous platforms

Author: Thomalla, Sandy J ; Moutier, William ; Ryan-Keogh, Thomas J ; Gregor, Luke ; Schutt, Julia Date: Dec 2017 Autonomous platforms will begin to address the space-time gaps required to improve estimates of phytoplankton distribution, which will aid in the quantification of baseline conditions necessary to detect long-term trends that can be attributed ... Read more
Phytoplankton chemotaxonomy in the Atlantic sector of the Southern Ocean during late summer 2009

Author: Gibberd, M-J ; Kean, E ; Barlow, R ; Thomalla, Sandy J ; Lucas, M Date: Aug 2013 A chemotaxonomic investigation of surface phytoplankton was undertaken on a research cruise to the Atlantic sector of the Southern Ocean during late austral summer 2009. Based on pigment signatures, several distinct regions emerged that were ... Read more
Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters

Author: Thomalla, Sandy J ; Waldron, HN ; Lucas, MI ; Read, JF ; Ansorge, IJ ; Pakhomov, E Date: 2010 During the 1999 Marion Island Oceanographic Survey (MIOS 4) in late austral summer, a northbound and reciprocal southbound transect were taken along the Southwest Indian and Madagascar Ridge, between the Prince Edward Islands and 31° S. The ... Read more
Phytoplankton response in growth, photophysiology and community structure to iron and light in the Polar Frontal Zone and Antarctic waters

Author: Viljoen, JJ ; Philibert, R ; Van Horsten, Natasha R ; Mtshali, Thato N ; Roychoudhury, AN ; Thomalla, Sandy J ; Fietz, S Date: Nov 2018 Availability of dissolved iron and light are both regulating factors for primary productivity in high (macro) nutrient, low chlorophyll regions of the Southern Ocean. Here, using on-board iron/light incubation experiments conducted in 2015 ... Read more
Recommendations for plankton measurements on OceanSITES moorings with relevance to other observing sites

Author: Boss, E ; Waite, AM ; Karstensen, J ; Trull, T ; Muller-Karger, F ; Sosik, HM ; Uitz, J ; Acinas, SG ; Acinas, SG ; Fennel, K ; Thomalla, Sandy J Date: Dec 2022 Measuring plankton and associated variables as part of ocean time-series stations has the potential to revolutionize our understanding of ocean biology and ecology and their ties to ocean biogeochemistry. It will open temporal scales (e.g., ... Read more
Remote sensing of phytoplankton community composition in the northern Benguela upwelling system

Author: Moloto, Tebatso M ; Thomalla, Sandy J ; Smith, Marie E ; Martin, B ; Louw, DC ; Koppelmann, R Date: Sep 2023 Marine phytoplankton in the northern Benguela upwelling system (nBUS) serve as a food and energy source fuelling marine food webs at higher trophic levels and thereby support a lucrative fisheries industry that sustain local economies in ... Read more
Sea-ice impacts inter-annual variability in bloom phenology and carbon export in the Weddell Sea

Author: Giddy, IS ; Nicholson, Sarah-Anne ; Queste, RY ; Thomalla, Sandy J ; Swart, S Date: Aug 2023 The Antarctic Marginal Ice Zone (MIZ) accounts for 15% of the Southern Ocean's primary production (PP), but limited data has hindered understanding of its variability and connection to carbon export. Using a combination of gliders, biogeochemical ... Read more
The seasonal cycle of mixed layer dynamics and phytoplankton biomass in the Sub-Antarctic Zone: A high-resolution glider experiment

Author: Swart, S ; Thomalla, Sandy J ; Monteiro, Pedro MS Date: Jun 2014 In the Southern Ocean there is increasing evidence that seasonal to subseasonal temporal scales, meso- and submesoscales play an important role in understanding the sensitivity of ocean primary productivity to climate change. In this study, ... Read more
The seasonal cycle of nitrogen uptake and nitrification in the Atlantic sector of the Southern Ocean

Author: Mdutyana, M ; Thomalla, Sandy J ; Philibert, R ; Ward, BB ; Fawcett, SE Date: Jul 2020 Net primary production (NPP) fueled by nitrate is often equated with carbon export, providing a metric for CO2 removal to the deep ocean. This “new production paradigm” assumes that nitrification, the oxidation of regenerated ammonium to ... Read more
Seasonal development of iron limitation in the sub-Antarctic zone

Author: Ryan-Keogh, Thomas J ; Thomalla, Sandy J ; Mtshali, Thato N ; Van Horsten, Natasha R ; Little, HJ Date: Jul 2018 The seasonal and sub-seasonal dynamics of iron availability within the sub-Antarctic zone (SAZ; 40–45 degees) play an important role in the distribution, biomass and productivity of the phytoplankton community. The variability in iron ... Read more

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