An integrated approach to pathogen transmission via environmental reservoirs

To mitigate the effects of zoonotic diseases on human and animal populations, it is critical to understand what factors alter transmission dynamics. Here we assess the risk of exposure to lethal concentrations of the anthrax bacterium, Bacillus anthracis, for grazing animals in a natural system over time through different transmission mechanisms. We follow pathogen concentrations at anthrax carcass sites and waterholes for five years and estimate infection risk as a function of grass, soil or water intake, age of carcass sites, and the exposure required for a lethal infection. Grazing, not drinking, seems the dominant transmission route, and transmission is more probable from grazing at carcass sites 1–2 years of age. Unlike most studies of virulent pathogens that are conducted under controlled conditions for extrapolation to real situations, we evaluate exposure risk under field conditions to estimate the probability of a lethal dose, showing that not all reservoirs with detectable pathogens are significant transmission pathways

From transparency to accountability of intelligent systems: Moving beyond aspirations

A number of governmental and nongovernmental organizations have made significant efforts to encourage the development of artificial intelligence in line with a series of aspirational concepts such as transparency, interpretability, explainability, and accountability. The difficulty at present, however, is that these concepts exist at a fairly abstract level, whereas in order for them to have the tangible effects desired they need to become more concrete and specific. This article undertakes precisely this process of concretisation, mapping how the different concepts interrelate and what in particular they each require in order to move from being high-level aspirations to detailed and enforceable requirements. We argue that the key concept in this process is accountability, since unless an entity can be held accountable for compliance with the other concepts, and indeed more generally, those concepts cannot do the work required of them. There is a variety of taxonomies of accountability in the literature. However, at the core of each account appears to be a sense of “answerability”; a need to explain or to give an account. It is this ability to call an entity to account which provides the impetus for each of the other concepts and helps us to understand what they must each require

A First Global Oceanic Compilation of Observational Dissolved Aluminum Data With Regional Statistical Data Treatment

Large national and international observational efforts over recent decades have provided extensive and invaluable datasets of a range of ocean variables. Compiled large datasets, structured, or unstructured, are a powerful tool that allow scientists to access and synthesize data collected over large spatial and temporal scales. The data treatment approaches for any element in the ocean could lead to new global perspectives of their distribution patterns and to a better understanding of large-scale oceanic processes and their impact on other biogeochemical cycles, which may not be evident otherwise. Ocean chemistry Big Data analysis may not just be limited to distribution patterns, but may be used to assess how sampling efforts and analytical methodologies can be improved. Furthermore, a systematic global scale assessment of data is important to evaluate the gaps in knowledge and to provide avenues for future research. In this context, here we provide an extensive compilation of oceanic aluminum (Al) concentration data from global ocean basins, including data available in the GEOTRACES Intermediate Data product (Schlitzer et al., 2018), but also thus far unpublished data

Measurement of bioactive trace metals (Cu and Zn) in the Southern Ocean : validation of sampling protocol and ICP-MS based analytical method

Thesis (MSc)--Stellenbosch University, 2017.ENGLISH ABSTRACT: A method comprising an improved seawater collection protocol and subsequent Inductively Coupled Plasma Mass Spectrometry (ICP-MS) based analytical technique was validated through an intercalibration exercise performed with the University of Plymouth (UK), multiple cross-over stations and analyses of certified reference materials (SAFe, GEOTRACES and NASS-5). The commercially available seaFAST-pico preconcentration module was employed for the simultaneous extraction of a suite of trace metals (Mn, Fe, Ni, Cu, Zn, Co, Cd and Pb) from their seawater matrix prior to ICP-MS analysis. Extremely low detection limits (< 0.228 nmol/kg) combined with low blank values ensured quantitive recovery on ICP-MS and minimal interferences arising from alkali and alkaline earth metals (Na, K, Mg and Ca) present in the saline matrix. The results of the certified reference materials were in excellent agreement with their corresponding consensus values and validated the methods precision and accuracy. During ICP-MS analysis, repeatability and reproducibility were monitored through analysis of an internal Stellenbosch University (SU) TM4 control and various commercially available quality controls, the results of which further confirmed a high level of precision. The distribution of Dissolved Copper (DCu) and Dissolved Zinc (DZn) was investigated in the Atlantic sector of the Southern Ocean. DCu displayed typical nutrient type behaviour reflected by sub-nanomolar surface concentrations increasing steadily until maximum observed concentrations of 2 – 3 nmol/kg in the Antarctic Bottom Waters (AABW). DZn concentrations ranged between approximately 1 and 12 nmol/kg and exhibited characteristic nutrient-type behaviour although intermediate and deepwater distributions were more conservative compared to DCu. Local subsurface minima coincided with elevated levels of chlorophyll-a (chl-a) indicating biological utilisation by phytoplankton in the euphotic zone. Remineralisation of sinking organic matter, predominantly diatom frustules, from Antarctic Surface Water (AASW) resulted in deeper sub-surface maxima for DZn. The dominant supply of trace metals to surface waters south of the Antarctic Polar Front (APF) was advective upwelling of nutrient rich Upper Circumpolar Deep Water (UCDW) and AABW. Atmospheric inputs and melting ice accounted for minor surface influxes where there was a poor DCu/salinity correlation. Both trace elements displayed significant correlations with the macronutrient silica, evidence of their role in the biological cycle. An overall Cu:Si relationship of Cu (nM) = 0.011 Si (μM) + 0.851 (R2 = 0.85, n=98) was obtained for this study while the corresponding Zn:Si relationship was Zn (nM) = 0.043 Si (μM) + 1.021 (R2 = 0.80, n=98). The APF exerted a strong control over nutrient distributions separating low nutrient low chlorophyll (LNLC) subtropical waters to the north from high nutrient low chlororphyll (HNLC) waters to the south. Keywords: Southern Ocean, Dissolved Copper, Dissolved Zinc, GEOTRACES, seaFAST, ICP-MSAFRIKAANSE OPSOMMING: 'n Metode wat bestaan uit 'n verbeterde seewater versameling protokol en die daaropvolgende Inductively Coupled Plasma Mass Spectrometry (ICP-MS) gebaseer analitiese tegniek is bekragtig deur 'n onderlinge oefening uitgevoer met die Universiteit van Plymouth (UK), verskeie ‘cross-over’ stasies en ontleding van gesertifiseerde verwysingsmateriaal (SAFe, GEOTRACES en NASS-5). Die kommersieel beskikbare seaFAST-pico preconcentration module is aangewend vir die gelyktydige onttrekking van 'n versameling van spoor metale (Mn, Fe, Ni, Cu, Zn, Co, Cd en Pb) van hul seewater matriks voor ICP-MS analise. Uiters lae opsporings perke (<0,228 nmol / kg) gekombineer met 'n lae leegwaardes verseker kwantitatiewe herstel op ICP-MS en minimale inmenging wat voortspruit uit alkalie en alkalie-aard metale (Na, K, Mg en Ca) teenwoordig is in die sout matriks. Die resultate van die gesertifiseerde verwysingsmateriaal was in 'n uitstekende ooreenkoms met hul ooreenstemmende konsensuswaardes en bekragtig die presisie en akkuraatheid van die metodes. Tydens ICP-MS analise, herhaalbaarheid en reproduseerbaarheid is gemonitor deur analise van 'n interne Universiteit Stellenbosch (US) TM4- beheer en verskeie kommersieel beskikbare kwaliteit beheer, die resultate waarvan 'n hoë vlak van akkuraatheid verder bevestig. Die verspreiding van opgeloste Koper (DCu) en opgeloste Zinc (DZn) is ondersoek in die Atlantiese sektor van die Suidelike Yssee. DCu vertoon tipiese tipe voedingstofagtige gedrag weerspieël deur sub-nanomolar oppervlak konsentrasies steeds toenemende tot maksimum waargenome konsentrasies van 2 - 3 nmol / kg in die Antarctic Bottom Waters (AABW). DZn konsentrasies wissel tussen ongeveer 1 en 12 nmol / kg en vertoon voedingstofagtige gedrag hoewel intermediêre- en diepwaterverspreidings meer konserwatief in vergelyking met DCu was. Plaaslike ondergrondse minima saamgeval met verhoogde vlakke van chlorofil-a (Chl-a) dui biologiese benutting deur fitoplankton in die euphotic sone aan. Remineralisasering van sink organiese materiaal, hoofsaaklik diatom frustules van Antarctic Surface Water (AASW) tot gevolg gehad vir ‘n dieper sub-oppervlak maksima vir DZn. Die dominante verskaffing van spoor metale om water oppervlak suid van die Antarctic Polar Front (APF) was advektiewe opwelling van voedingstofryke Upper Circumpolar Deep Water (UCDW) en AABW. Atmosferiese insette en smeltingsys is verantwoordelik vir klein oppervlak strome waar daar was 'n swak DCu / soutgehalte korrelasie. Beide spoorelemente vertoon beduidende korrelasies met die makro-silika, bewyse van hul rol in die biologiese siklus. 'N Algehele Cu:Si verhouding van Cu (nM) = 0,011 Si (μm) + 0,851 (R2 = 0.85, n = 98) is verkry vir hierdie studie, terwyl die ooreenstemmende Zn: Si verhouding was Zn (nM) = 0,043 Si (μM ) + 1,021 (R2 = 0.80, n = 98). Die APF oefen sterk beheer uit oor voedingstof verspreiding wat low nutrient low chlorophyll (LNLC) subtropiese waters in die noorde skei high nutrient low chlorophyll (HNLC) water na die suide. Trefwoorde: Suidelike Yssee, opgeloste Koper, opgeloste Zinc, GEOTRACES, seaFAST, ICP-M

On the distribution and biogeochemical cycling of bioactive trace metals in the Southern Ocean

Thesis (PhD)--Stellenbosch University, 2020.ENGLISH ABSTRACT: Bioactive trace metals, including copper (Cu), zinc (Zn), nickel (Ni) and cadmium (Cd), are essential micronutrients to marine phytoplankton and their availability in the surface ocean has been shown to influence phytoplankton community composition and abundance. Through photosynthesis, phytoplankton are the primary drivers of the marine carbon cycle therefore constraining trace metal – phytoplankton dynamics, as well as other biogeochemical processes controlling trace metal distributions, is critical to understanding the greater carbon cycle. Owing to logistical constraints, less attention has been directed toward trace metal cycling on a seasonal basis. This is particularly important in the high latitude ocean regions where large seasonal fluctuations in environmental conditions e.g. light, wind and temperature, are likely to impact trace metal distributions directly or indirectly. To this end, this study focuses on the data scarce Southern Ocean and investigates the distribution and biogeochemical cycling of Cu, Zn, Ni and Cd in summer and in winter, two seasons with contrasting environmental conditions for phytoplankton growth. This framework provided a unique opportunity to characterise the Southern Ocean winter reset period and to assess the role of deep winter mixing as a potential in-situ physical trace metal supply mechanism to aid surface productivity. In order to address these questions, research cruises were conducted in summer and winter in the Atlantic sector of the Southern Ocean (0 - 8°E) while a third cruise took place in winter in the Indian Sector of the Southern Ocean (30°E). In the Atlantic sector, first winter measurements of dissolved (0.2 µm filtered seawater) Cu (dCu), Zn (dZn) and Ni (dNi) were compared with corresponding summer measurements from the same locations. Differences in trace metal distributions were most evident in the surface mixed layer where winter concentrations were consistently greater compared to summer. Variations in trace metal seasonality were also linked to latitude whereby seasonal variations observed near the Sub-Antarctic Front (SAF; ~ 46°S) were negligible for all three trace metals and largest variations, up to 2.0 nmol kg⁻¹ for dCu, 1.2 nmol kg⁻¹ for dZn and 0.3 nmol kg⁻¹ for dNi, were observed near the southern extent of the Antarctic Circumpolar Current (ACC; ~ 54°S). The primary driver of these variations was through differences in biological activity with lower trace metal utilisation during winter. Sub-optimal growth conditions experienced by phytoplankton during the winter were further confirmed through calculated trace metal uptake ratios and estimations of phytoplankton productivity. Our results further suggest that deep winter mixing, i.e. the mixing of depleted summer surface waters with nutrient enriched sub-surface waters, constitutes a potentially significant surface water source of dCu, dZn and dNi with implications for phytoplankton productivity over the subsequent spring and summer seasons. In the Indian sector of the Southern Ocean (30°E longitude), winter measurements of dZn and dissolved cadmium (dCd) were coupled with particulate (> 0.45 µm filter) zinc (pZn) and cadmium (pCd) in an effort to investigate winter trace metal cycling in more detail. Distinct changes in dissolved and particulate Cd and Zn cycling were observed between the various frontal regions encountered and were related to changes in phytoplankton community composition and physical circulation patterns. Our data suggests diatoms are major drivers of the observed trace metal gradients through their preferential consumption of dCd and dZn, relative to the major nutrient phosphate (PO4), in the Antarctic Zone (AAZ). Here, high dCd/PO4 and dZn/PO4 uptake ratios set the high ratios of pCd and pZn to phosphorous (P; pCd/P; pZn/P) observed in surface waters. Ultimately, the uptake characteristics of diatoms at higher latitudes influences Cd and Zn cycling at lower latitudes as a result of the northward flow of surface waters depleted in dCd and dZn. In addition, because diatoms require silicic acid (Si(OH)4), the export of their cells below the winter mixed layer provides additional insights as to the observed deep water coupling of dZn and Si(OH)4. Below the surface, Cd and Zn cycling is predominantly controlled by remineralisation, vertical mixing and upwelling. We conclude that winter Southern Ocean surface waters are not biologically dormant and that trace metal cycling is influenced by biological productivity during winter.AFRIKAANSE OPSOMMING: Bio-aktiewe spoormetale, insluitend koper (Cu), sink (Zn), nikkel (Ni) en kadmium (Cd), is noodsaaklike mikrovoedingstowwe vir mariene fitoplankton. Daar word getoon dat die beskikbaarheid van hierdie bio-aktiewe spoormetale in die oppervlakwater van die oseaan die fitoplanktongemeenskappe se samestelling en weligheid beïnvloed. Fitoplankton is die primêre dryfveer vir die mariene koolstofsiklus deur fotosintese. Die ontleding van die dinamika tussen spoormetale en fitoplankton, asook die ander biogeochemiese prosesse wat die verspreiding van spoormetale beheer, is kritiek tot die verstaan van die groter koolstofkringloop. Seisoenaal word daar minder aandag gegee aan spoormetaal-siklussering as gevolg van logistieke beperkinge, veral in die hoë breedtegraad oseaanstreke. In hierdie streke is die kanse groter dat die verspreiding van spoormetale direk of indirek beïnvloed word deur die groot seisoenale skommelinge in omgewingstoestande soos lig, wind en temperatuur. Derhalwe fokus hierdie studie op die Suidelike Oseaan waaroor daar ‘n skaarste aan data is en ondersoek dit die verspreiding en biogeochemiese siklussering van Cu, Zn, Ni en Cd in die somer en winter, twee seisoene met uiteenlopende omgewingstoestande vir die groei van fitoplankton. Hierdie raamwerk bied ‘n unieke geleentheid om die tydperk van herset tydens die winter in die Suidelike Oseaan te karakteriseer en die rol van diepte-vermenging in die winter as ‘n potensiële meganisme om ter plaatse spoormetale te voorsien wat produktiwiteit in die oppervlakwater van die oseaan bevorder, te bepaal. Ten einde hierdie vrae aan te spreek, is navorsingsvaarte tydens somer- en wintermaande in die Atlantiese gedeelte van die Suidelike Oseaan (0 - 8°E) uitgevoer. ‘n Derde navorsingsvaart het tydens die winter in die Indiese gedeelte van die Suidelike Oseaan (30°E) plaasgevind. In die Atlantiese gedeelte is die metings van opgeloste (0.2 µm gefiltreerde seewater) Cu (dCu), Zn (dZn) and Ni (dNi), wat vir die eerste keer tydens die winter geneem is, vergelyk met die ooreenstemmende metings wat in die somer by dieselfde ligging geneem is. Die verskil in die verspreiding van die spoormetale was die duidelikste in die oppervlakmenglaag. Hier was die konsentrasies, wat in die winter gemeet is, deurgaans hoër as in die somer. Variasies in die seisoensgebondenheid van spoormetale is ook aan breedteligging verbind. Die veranderinge wat tydens die seisoenskommeling by die Subantarktiese Front (SAF; ~ 46°S) waargeneem is, was weglaatbaar klein vir al drie spoormetale. Die grootste variasies, tot 2.0 nmol kg⁻¹ vir dCu, 1.2 nmol kg⁻¹ vir dZn en 0.3 nmol kg⁻¹ vir dNi, is naby die suidelike reikwydte van die Antarktiese Sirkumpolêre Seestroom (ACC; ~ 54°S) waargeneem. Die hoofdryfveer van hierdie variasies was deur die verskil in biologiese aktiwiteit, met ‘n laer benutting van spoormetale in die winter. Die fitoplankton het in die winter suboptimale toestande vir groei ervaar, iets wat verder bevestig is deur die berekening van die verhoudings van spoormetale se opname en die skattinge rakende die produktiwiteit van die fitoplankton. Ons uitslae dui verder daarop dat die diepte- vermenging in die winter, m.a.w. die vermenging van die uitgeputte oppervlakwater van die oseaan van die somerseisoen met die dieper water wat verryk is met voedingstowwe, moontlik ‘n beduidende bron van dCu, dZn and dNi in die oppervlakwater van die oseaan uitmaak. Dit het implikasies vir fitoplanktonproduktiwiteit gedurende die daaropvolgende lente en somer. In die Indiese gedeelte van die Suidelike Oseaan (30°E lengtegraad), is die metings van dZn en opgeloste kadmium (dCd) wat in die winter gemeet is, verbind met partikulêre (> 0.45 µm filter) sink (pZn) en kadmium (pCd) in ‘n poging om spoormetaal-siklussering in die winter in meer diepte te ondersoek. Onmiskenbare veranderinge in die opgeloste en partikulêre Cd en Zn siklussering is tussen die verskeie frontale streke waargeneem. Dit is verwant aan die veranderinge in die samestelling van die fitoplanktongemeenskappe en die fisiese sirkulasiepatrone. Volgens ons data is diatomeë die hoofaandrywers van die gradiënte van die spoormetale se konsentrasies wat waargeneem is. Dit is oorwegend as gevolg van diatomeë se voorkeur vir die verbruik van dCd and dZn, relatief tot fosfaat (PO4) as die vername voedingstof in die Antarktiese Zone (AAZ). Hier word daar in die oppervlakwater van die oseaan waargeneem dat hoë verhoudings van dCd/PO4 en dZn/PO4 se opname lei tot hoë verhoudings van pCd en pZn tot fosfor. Uiteindelik beïnvloed die kenmerkende manier waarop diatomeë hierdie spoormetale opneem by hoër breedteliggings die siklussering van Cd en Zn by laer breedteliggings as gevolg van die noordwaartse vloei van die oppervlakwater van die oseaan wat uitgeput is aan dCd en dZn. Boonop verskaf die besinking van diatomeë tot onder die menglaag in die winter verdere insigte oor die aankoppeling wat tussen dZn en kieselsuur (Si(OH)4) waargeneem word, aangesien diatomeë kieselsuur benodig. Onder die oppervlak menglaag word die siklussering van Cd en Zn oorwegend deur hermineralisering, vertikale vermenging en opwelling beheer. Ons kom tot die gevolgtrekking dat die oppervlakwater van die Suidelike Oseaan nie in die winter biologies onaktief is nie en dat spoormetaal-siklussering gedurende die winter deur biologiese produktiwiteit beïnvloed word.Doctora

Determination of Trace Metal (Mn, Fe, Ni, Cu, Zn, Co, Cd and Pb) Concentrations in Seawater Using Single Quadrupole ICP-MS: A Comparison between Offline and Online Preconcentration Setups

The quantification of dissolved metals in seawater requires pre-treatment before the measurement can be done, posing a risk of contamination, and requiring a time-consuming procedure. Despite the development of automated preconcentration units and sophisticated instruments, the entire process often introduces inaccuracies in quantification, especially for low-metal seawaters. This study presents a robust method for measuring dissolved metals from seawater accurately and precisely using a seaFAST and quadrupole Inductively Coupled Plasma Mass Spectrometer (ICPMS), employed in both offline (2016–2018) and online (2020–2021) setups. The proposed method shows data processing, including the re-calculation of metals after eliminating the instrumental signals caused by polyatomic interferences. Here, we report the blank concentration of Fe below 0.02 nmol kg−1, somewhat lower values than that have been previously reported using high-resolution and triple-quad ICPMS. The method allows for the accurate determination of Cd and Fe concentrations in low-metal seawaters, such as GEOTRACES GSP, using a cost-effective quadrupole ICPMS (Cdconsensus: 2 ± 2 pmol kg−1, Cdmeasured: 0.99 ± 0.35 pmol kg−1; Feconsensus: 0.16 ± 0.05 nmol kg−1, Femeasured: 0.21 ± 0.03 nmol kg−1). Between two setups, online yields marginally lower blank values for metals based on short-term analysis. However, the limit of detection is comparable between the two, supporting optimal instrumental sensitivity of the ICPMS over 4+ years of analysis

Links between the phytoplankton community composition and trace metal distribution in summer surface waters of the Atlantic Southern Ocean

CITATION: Viljoen, J. J., et al. 2019. Links between the phytoplankton community composition and trace metal distribution in summer surface waters of the Atlantic Southern Ocean. Frontiers in Marine Science, 6:295, doi:10.3389/fmars.2019.00295.The original publication is available at https://www.frontiersin.orgPublication of this article was funded by the Stellenbosch University Open Access Fund.This study assessed changes in the phytoplankton community related to macronutrient and bioactive trace metal distribution in surface waters of the Atlantic sector of the Southern Ocean, between Cape Town and Antarctica along the GEOTRACES GIPY_05 (mainly along prime meridian) transect in summer 2014–2015. Several general community structure features were reaffirmed, such as the restriction of cyanobacteria to the northern Subtropical Zone, while haptophytes, such as Phaeocystis, along with diatoms, dominate the community north of the Polar Front, and diatoms clearly dominate south of the Polar Front. These community structure changes were often linked with macro- and micro-nutrient composition changes. For example, the concentration of diatoms increased southwards with the availability of silica whereas the cyanobacterial contribution in the northern Subtropical Zone appeared to be linked with labile cobalt depletion. However, these links were not consistent along the entire transect, i.e., no individual nutrient, such as silica or iron, was linked to community composition changes across all water masses. Each station showed a rather unique combination of nutrient and community compositions. Our findings also indicated impacts on the phytoplankton community through trace metal distributions that could be related to a deep mixing event at ∼54∘S and to ice melt at ∼65 and 68∘S. The timing of sampling after such trace metal fluxes proved to be an important consideration, particularly where iron appeared to be preferentially depleted to near-limiting concentrations, possibly driving utilization of other metals. The study highlights the importance of considering a suite of trace metals when assessing controls of phytoplankton variability in the open ocean and emphasizes the need for higher resolution trace metal sampling and multi-element incubation studies to further study the complex relationships between phytoplankton and nutrients.https://www.frontiersin.org/articles/10.3389/fmars.2019.00295/fullPublisher's versio

From transparency to accountability of intelligent systems

A number of governmental and non-governmental organisations have made significant efforts to encourage the development of artificial intelligence in line with a series of aspirational concepts such as transparency, interpretability, explainability and accountability. The difficulty at present, however, is that these concepts exist at a fairly abstract level, whereas in order for them to have the tangible effects desired they need to become more concrete and specific. This paper undertakes precisely this process of concretisation, mapping how the different concepts interrelate and what in particular they each require in order to move from being high-level aspirations to detailed and enforceable requirements. We argue that the key concept in this process is accountability, since unless an entity can be held accountable for compliance with the other concepts, and indeed more generally, those concepts cannot do the work required of them. There is a variety of taxonomies of accountability in the literature. However, at the core of each account appears to be a sense of ‘answerability’; a need to explain or to give an account. It is this ability to call an entity to account which provides the impetus for each of the other concepts and helps us to understand what they must each require

Winter Biogeochemical Cycling of Dissolved and Particulate Cadmium in the Indian Sector of the Southern Ocean (GEOTRACES GIpr07 Transect)

Winter distributions of dissolved cadmium (dCd) and particulate cadmium (pCd) were measured for the first time in the Indian sector of the Southern Ocean thereby contributing a unique spatial and seasonal dataset. Seven depth profiles, between 41°S and 58°S, were collected along the 30°E longitude during the 2017 austral winter to investigate the biogeochemical cycling of cadmium during a period characterized by contrasting upper water column dynamics compared to summer. Our results support an important role for biological uptake during winter months albeit weaker compared to summer. Distinct, biologically driven changes in cadmium cycling across the transect were observed. For example, surface ratios of pCd to phosphorus (P; pCd:P) increased from 0.37 to 1.07 mmol mol–1 between the subtropical zone (STZ) and the Antarctic zone (AAZ) reflecting increased Cd requirements for diatoms at higher latitudes which, in turn, was driven by a complex relationship between the availability of dCd and dissolved iron (dFe), zinc (dZn) and manganese (dMn). Vertical profiles of pCd:P displayed near-surface maxima consistent with (1) P occurring in two phases with different labilities and the lability of Cd being somewhere in-between and (2) increasing dCd to phosphate (PO4; dCd:PO4) ratios with depth at each station. North of the Antarctic Polar Front (APF), a secondary, deeper pCd:P maximum may reflect an advective signal associated with northward subducting Antarctic Intermediate Water (AAIW). The strong southward increase in surface dCd and dCd:PO4, from approximately 10–700 pmol kg–1 and 40–400 μmol mol–1, respectively, reflected the net effect of preferential uptake and regeneration of diatoms with high Cd content and the upwelling of Cd enriched water masses in the AAZ. Furthermore, distinct dCd versus PO4 relationships were observed in each of the intermediate and deep water masses suggesting that dCd and PO4 distributions at depth are largely the result of physical water mass mixing