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

Jan-Lukas Menzel Barraqueta, Saumik Samanta, Eric P Achterberg, Andrew

R Bowie, Peter Croot, Ryan Cloete, Tara de Jongh, Maria D

Gelado-Caballero, Jessica K Klar, Rob Middag, et al.

► To cite this version:

Jan-Lukas Menzel Barraqueta, Saumik Samanta, Eric P Achterberg, Andrew R Bowie, Peter Croot, et al.. A First Global Oceanic Compilation of Observational Dissolved Aluminum Data With Regional Statistical Data Treatment. Frontiers in Marine Science, 2020, 7, 10.3389/fmars.2020.00468. hal-04200055

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

Jan-Lukas Menzel Barraqueta<fnref n="1" />*, Saumik Samanta<fnref n="1" />, Eric P. Achterberg², Andrew R. Bowie³,⁴, Peter Croot⁵, Ryan Cloete<fnref n="1" />, Tara De Jongh<fnref n="1" />, Maria D. Gelado-Caballero⁶, Jessica K. Klar⁷, Rob Middag⁸, Jean C. Loock<fnref n="1" />, Tomas A. Remenyi³,⁴, Bernhard Wenzel<fnref n="1" />,² and Alakendra N. Roychoudhury<fnref n="1" />

## OPEN ACCESS

**Edited by:**
Antonio Tovar-Sanchez
Consejo Superior de Investigaciones
Científicas (CSIC), Spain

**Reviewed by:**
Mariko Hatta
University of Hawaii, United States
Maxime M. Grand,
Moss Landing Marine Laboratories,
United States

*Correspondence:
Jan-Lukas Menzel Barraqueta
jmenzel@sun.ac.za

**Specialty section:**
This article was submitted to Marine Biogeochemistry, a section of the journal Frontiers in Marine Science

**Received:** 24 February 2020

**Accepted:** 26 May 2020

**Published:** 14 July 2020

**Citation:**
Menzel Barraqueta J-L, Samanta S, Achterberg EP, Bowie AR. Croot P, Cloete R, De Jongh T, Gelado-Caballero MD, Klar JK, Middag R, Loock JC, Remenyi TA, Wenzel B and Roychoudhury AN. (2020) A First Global Oceanic Compilation of Observational Dissolved Aluminum Data With Regional Statistical Data Treatment. Front. Mar. Sci. 7:468. doi: 10.3389/fmars.2020.00468

**Keywords:** database, oceans, aluminum, compilation, biogeochemistry, GEOTRACES

## INTRODUCTION

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.

Aluminum is the third most abundant element in the continental crust (Wedepohl, 1995), but is only found in trace amounts in seawater. Aluminum is supplied to the oceans through atmospheric deposition, hydrothermal venting, sediment resuspension, diffusion from sediment pore waters, and continental drainage (e.g., fluvial). The element is a widely used tracer of atmospheric deposition to the surface ocean (Measures and Brown, 1996; Measures and Vink, 2000; Grand et al., 2015a; Menzel Barraqueta et al., 2019), and is also used as a tracer of water masses and input sources (Measures and Edmond, 1990; Brown et al., 2010; Resing et al., 2015; Menzel Barraqueta et al., 2018). Dissolved Al (dAl) is particle reactive, and displays a scavenged-type vertical profile in many ocean regions (Bruland et al., 2013). However, recent dissolved Al data reveal that this element also displays a recycled or reversible scavenging type distribution in certain ocean regions (Van Hulten et al., 2013; Rolison et al., 2015; Menzel Barraqueta et al., 2018). Since the first publication on Al concentrations in seawater [(Hydes, 1979); sampling year 1973], sampling

<footnote n="1">¹Department of Earth Sciences, Stellenbosch University, Stellenbosch, South Africa, ²GEOMAR, Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, ³Antarctic Climate and Ecosystems—Cooperative Research Centre, University of Tasmania, Hobart, TAS, Australia, ⁴Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia, ⁵ICRAG (Irish Centre for Research in Applied Geoscience), Earth and Ocean Sciences, School of Natural Sciences and the Ryan Institute, National University of Ireland Galway, Galway, Ireland, ⁶Chemistry Department, University of las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain, ⁷CEFREM, University of Perpignan Via Domitia, CNRS, IRD, Perpignan, France, ⁸Department of Ocean Systems (OCS), NIOZ Royal Netherlands Institute for Sea Research, and Utrecht University, Texel, Netherlands</footnote>
and analytical techniques [review in (Tria et al., 2007)] have improved, contamination risks have been reduced, and analytical precision, accuracy and detection limit improved. For example, the introduction of a solid-phase extraction method (Resing and Measures, 1994) with further optimizations (Brown and Bruland, 2008) have yielded detection limits at the sub-nanomolar level (e.g., 0.1 nM) which are lower than previous values (e.g., 1.85 nM, Hydes and Liss, 1976). This may indicate lower Al concentrations measured in recent years (see section Data Variability Over Time). Dissolved Al is defined as the Al concentration in the filtered fraction (filter cut-off 0.2–0.45 µm) of a solution. Studies have shown that only a small percentage of dAl is present in the colloidal phase in open ocean waters (Dammshäuser and Croot, 2012) and that Al concentrations in unfiltered and unacidified samples measured onboard shortly after collection are consistent with those from filtered samples as the dissolution of particulate Al is negligible at the pH of natural seawater (Measures et al., 1986). As a result of the development of intercalibration exercises [e.g., SAFE, (Johnson et al., 2007)] and best sampling practices and protocols (e.g., GEOTRACES Cookbook, www.geotraces.org) a recommendation on filtration protocols for all trace metals has been adopted in order to ensure data comparability among different groups. In this manuscript we focus on dAl and make the simple assumption that the strong vertical and basin-scale gradients in dAl concentrations within the ocean are larger than the systematic differences between unfiltered (unacidified and measured shortly after collection) and filtered samples.

The aim of this manuscript is to provide the scientific community with a global oceanic dAl database containing historical and recent data. We provide general global statistics with a focus on spatial, temporal and seasonal dAl variability. There is no intention to create a fully calibrated database, since this has only become possible in recent years due to the efforts made by the GEOTRACES programme (Frank et al., 2003) that aims to provide the scientific community with inter-calibrated datasets in the form of intermediate data products (Mawji et al., 2015; Schlitzer et al., 2018). Nevertheless, having a readily accessible database, even if not fully intercalibrated, is fundamental for research and comparison purposes. We note that the amount of intercalibrated dAl data will steadily increase in the coming years as Al is a key parameter of the GEOTRACES programme.

## DESCRIPTION OF THE DATABASE

The global oceanic and coastal dAl database file (Oceanic_Al_Menzel.xlsx) compiled here is accessible via the following link (https://doi.org/10.25413/sun.12167877.v1). The database forms an extension of the data files gathered by Gehlen et al. (2003) and Van Hulten et al. (2013), who collated Al data while applying internally chosen quality standards for specific, purpose driven, modeling efforts. We note another modeling manuscript (Han et al., 2008), that also compiled Al oceanic data; however, none of these manuscripts provide publicly available Al data. The Al data compiled here includes a considerable amount of unpublished data (ca. 20%, **Table 1**) which will be useful for the community and may foster further scientific discussion. Unpublished data may not be reproduced

without prior permission from the respective data originator, whose details are found in the database file (fourth tab). We compiled data reported in published papers, data reported in publicly accessible data-bases and additionally data was obtained directly from researchers if quantitative Al data was not reported in a publication (a list of Al manuscripts whose data is not included can be found at the end of **Table 1**). Despite our best efforts to retrieve all available Al data by searching the literature and approaching researchers we cannot assert that all historical data is included in the data file (apart from the previous mentioned manuscripts). Thus, we encourage researchers to submit generated Al data (to JLMB) to keep updating the Al database.

The dataset presented here includes (1) open ocean Al data for all major oceans (Atlantic, Arctic, Indian, Pacific, and Southern Oceans), (2) semi- and enclosed basins such as the Mediterranean Sea, Black Sea, and Arabian Sea and (3) regions where Al data was collected in proximity to major sources such as hydrothermal vents, shelf regions and river outflows. In some instances, a dataset includes repeated sections such as the A16N cruise which was sampled in 2003 and 2013 (Measures et al., 2008a; Barrett et al., 2015) thus providing temporally different Al concentrations for the same coordinates. Data from process studies, which, for instance, sample the same region over a determined period of time have also been included. We have also included one study which was undertaken at the LOREX site in the Arctic Ocean while the ship was drifting (Moore, 1981). In the latter case we chose a point halfway between the start and the end of sampling as station coordinates. From the dataset, we have excluded Al in brackish to freshwater environments (< salinity 25). We acknowledge that the compilation of Al concentration data would be greatly improved by accompanying ancillary parameters such as salinity, temperature, and nutrients. This could help to better understand key processes occurring within the ocean and how these controls the distribution of Al therein.

The time span covered by the database ranges from 1973 to 2017. **Table 1** lists all the publications included in the database. Following publication, the file includes, if given, the following additional information for each dataset: station number, sampling year, vessel, location, analytical method, reference material, filtration, and publication reference. The file can be easily reorganized alphabetically or numerically under the following terms and options: Location (Atlantic, Arctic, Indian, Pacific, and Southern oceans, and Arabian, Black and Mediterranean Sea), reference material (Yes & No), filtration (Yes & No), sampling year etc. The dAl concentration is given in nanomolar (nM) units. In addition, a third tab records the changes made to the database following publication (e.g., in case new data are submitted).

## DATABASE

The data file contains 24,194 dAl data points and are presented in an alphabetical order in reference to the data originator. **Figure 1** shows graphical representations of the dAl concentration data included in the database. Below we provide three different sets of information; (i) general sampling efforts; (ii) global
<table><caption>TABLE 1 | Publications included in the database and ordered by year of sampling.</caption><thead><tr><th>Sampling year</th><th>Month</th><th>Ocean/Sea</th><th>Region</th><th>Filter (Yes/No)</th><th>Reference material</th><th>References</th></tr></thead><tbody><tr><td>1973</td><td>10</td><td>Atlantic</td><td>Central</td><td>N</td><td>N</td><td>Hydes, 1979</td></tr><tr><td>1976</td><td>5, 9</td><td>Mediterranean</td><td>-</td><td>Y</td><td>N</td><td>Stoffyn and Mackenzie, 1982</td></tr><tr><td>1977</td><td>4</td><td>Atlantic</td><td>Barbados</td><td>Y</td><td>N</td><td>Stoffyn and Mackenzie, 1982</td></tr><tr><td>1977</td><td>9</td><td>Atlantic</td><td>Central</td><td>N</td><td>N</td><td>Hydes, 1979</td></tr><tr><td>1978</td><td>7</td><td>Atlantic</td><td>-</td><td>Y</td><td>N</td><td>Stoffyn and Mackenzie, 1982</td></tr><tr><td>1979</td><td>3–5</td><td>Arctic</td><td>Central</td><td>N</td><td>N</td><td>Moore, 1981</td></tr><tr><td>1980</td><td>9, 10</td><td>Pacific</td><td>Northeast</td><td>Y</td><td>N</td><td>Orians and Bruland, 1986</td></tr><tr><td>1982</td><td>1, 2</td><td>Atlantic</td><td>Northeast</td><td>N</td><td>N</td><td>Hydes, 1983</td></tr><tr><td>1982</td><td>3, 4</td><td>Atlantic</td><td>Northeast</td><td>N</td><td>N</td><td>Kremling, 1985</td></tr><tr><td>1982</td><td>-</td><td>Atlantic</td><td>-</td><td>-</td><td>-</td><td>Moore and Millward, 1984</td></tr><tr><td>1983</td><td>7</td><td>Pacific</td><td>Northeast</td><td>Y</td><td>N</td><td>Orians and Bruland, 1986</td></tr><tr><td>1983</td><td>11</td><td>Atlantic</td><td>Northwest</td><td>N</td><td>N</td><td>Measures et al., 1984</td></tr><tr><td>1984</td><td>4, 5</td><td>Atlantic</td><td>Central</td><td>-</td><td>N</td><td>Hydes et al., 1986</td></tr><tr><td>1984</td><td>Monthly</td><td>Atlantic</td><td>Sargasso</td><td>-</td><td>-</td><td>Jickells et al., 1994</td></tr><tr><td>1984</td><td>7</td><td>Atlantic</td><td>North Sea</td><td>Y</td><td>N</td><td>Kremling and Hydes, 1988</td></tr><tr><td>1984</td><td>6, 7</td><td>Pacific</td><td>Northeast</td><td>Y</td><td>N</td><td>Orians and Bruland, 1986</td></tr><tr><td>1985</td><td>Monthly</td><td>Atlantic</td><td>Sargasso</td><td>-</td><td>-</td><td>Jickells et al., 1994</td></tr><tr><td>1987</td><td>7, 8</td><td>Indian</td><td>Arabian Sea</td><td>N</td><td>N</td><td>Narvekar and Singbal, 1993</td></tr><tr><td>1987</td><td>5, 6</td><td>Mediterranean</td><td>-</td><td>Y</td><td>N</td><td>Hydes et al., 1988</td></tr><tr><td>1988</td><td>10, 11</td><td>Indian</td><td>Arabian Sea</td><td>N</td><td>N</td><td>Narvekar and Singbal, 1993</td></tr><tr><td>1988</td><td>1–3</td><td>Atlantic</td><td>South</td><td>N</td><td>N</td><td>Measures and Edmond, 1990</td></tr><tr><td>1988</td><td>4</td><td>Atlantic</td><td>Northwest</td><td>Y and N</td><td>N</td><td>Moran and Moore, 1991</td></tr><tr><td>1988</td><td>1, 2</td><td>Indian</td><td>Arabian Sea</td><td>N</td><td>N</td><td>Upadhyay and Gupta, 1994</td></tr><tr><td>1988</td><td>11, 12, 1</td><td>Southern</td><td>-</td><td>N</td><td>N</td><td>Van Bennekom et al., 1991</td></tr><tr><td>1988</td><td>-</td><td>Mediterranean</td><td>West</td><td>Y</td><td>N</td><td>Chou and Wollast, 1997</td></tr><tr><td>1989</td><td>1</td><td>Southern</td><td>Weddell Sea</td><td>N</td><td>N</td><td>Moran et al., 1992</td></tr><tr><td>1989</td><td>7</td><td>Mediterranean</td><td>West</td><td>Y</td><td>N</td><td>Chou and Wollast, 1997</td></tr><tr><td>1990</td><td>5</td><td>Atlantic</td><td>Latitudinal</td><td>N</td><td>N</td><td>Helmers and Rutgers van der Loef, 1993</td></tr><tr><td>1990</td><td>10, 11</td><td>Atlantic</td><td>Latitudinal</td><td>N</td><td>N</td><td>Helmers and Rutgers van der Loef, 1993</td></tr><tr><td>1990</td><td>3</td><td>Atlantic</td><td>Eastern</td><td>Y</td><td>N</td><td>Measures, 1995</td></tr><tr><td>1990</td><td>4</td><td>Mediterranean</td><td>West</td><td>Y</td><td>N</td><td>Chou and Wollast, 1997</td></tr><tr><td>1991</td><td>2, 3</td><td>Southern</td><td>Weddell Sea</td><td>Y</td><td>N</td><td>Sanudo-Wilhelmy et al., 2002</td></tr><tr><td>1991</td><td>3</td><td>Atlantic</td><td>Northeast</td><td>N</td><td>N</td><td>Gelado-Caballero et al., 1996</td></tr><tr><td>1992</td><td>10, 11</td><td>Pacific</td><td>Coral & Tasman Sea</td><td>N</td><td>N</td><td>Obata et al., 2008</td></tr><tr><td>1993</td><td>8</td><td>Atlantic</td><td>North</td><td>Y and N</td><td>N</td><td>Hall and Measures, 1998</td></tr><tr><td>1993</td><td>3–5</td><td>Indian</td><td>Enderby & Crozet Basin</td><td>-</td><td>N</td><td>Van Beusekom et al., 1997</td></tr><tr><td>1994</td><td>7–9</td><td>Arctic</td><td>-</td><td>N</td><td>N</td><td>Measures, 1999</td></tr><tr><td>1995</td><td>1, 2</td><td>Indian</td><td>Arabian Sea</td><td>Y</td><td>N</td><td>Measures and Vink, 1999</td></tr><tr><td>1995</td><td>3, 4</td><td>Indian</td><td>Arabian Sea</td><td>Y</td><td>N</td><td>Measures and Vink, 1999</td></tr><tr><td>1995</td><td>5</td><td>Indian</td><td>Arabian Sea</td><td>N</td><td>N</td><td>Schüßler et al., 2005</td></tr><tr><td>1995</td><td>7</td><td>Indian</td><td>Arabian Sea</td><td>N</td><td>N</td><td>Schüßler et al., 2005</td></tr><tr><td>1995</td><td>7, 8</td><td>Indian</td><td>Arabian Sea</td><td>Y</td><td>N</td><td>Measures and Vink, 1999</td></tr><tr><td>1995</td><td>8, 9</td><td>Indian</td><td>Arabian Sea</td><td>Y</td><td>N</td><td>Measures and Vink, 1999</td></tr><tr><td>1995</td><td>10, 11</td><td>Indian</td><td>Arabian Sea</td><td>Y</td><td>N</td><td>Measures and Vink, 1999</td></tr><tr><td>1996</td><td>8, 9</td><td>Atlantic</td><td>Latitudinal</td><td>N</td><td>N</td><td>Bowie et al., 2002</td></tr><tr><td>1996</td><td>12</td><td>Atlantic</td><td>Northeast</td><td>N</td><td>N</td><td>Gelado-Caballero unpublished</td></tr></tbody></table>

(Continued)
<table><caption>TABLE 1 | Continued</caption><thead><tr><th>Sampling year</th><th>Month</th><th>Ocean/Sea</th><th>Region</th><th>Filter (Yes/No)</th><th>Reference material</th><th>References</th></tr></thead><tbody><tr><td>1996</td><td>7</td><td>Pacific</td><td>Western</td><td>Y</td><td>N</td><td>Obata et al., 2004</td></tr><tr><td>1996</td><td>5, 6</td><td>Atlantic</td><td>Latitudinal</td><td>Y</td><td>N</td><td>Vink and Measures, 2001</td></tr><tr><td>1997</td><td>2, 3</td><td>Indian</td><td>Arabian Sea</td><td>N</td><td>N</td><td>Schüßler et al., 2005</td></tr><tr><td>1997</td><td>7, 8</td><td>Atlantic</td><td>Northeast</td><td>N</td><td>N</td><td>Gelado-Caballero unpublished</td></tr><tr><td>1997</td><td>–</td><td>Southern</td><td>Pacific sector</td><td>Y</td><td>N</td><td>Measures unpublished jgofs</td></tr><tr><td>1998</td><td>–</td><td>Southern</td><td>Pacific sector</td><td>Y</td><td>N</td><td>Measures unpublished jgofs</td></tr><tr><td>1998</td><td>5, 6</td><td>Atlantic</td><td>Latitudinal</td><td>N</td><td>N</td><td>Bowie et al., 2002</td></tr><tr><td>1998</td><td>3</td><td>Atlantic</td><td>Northeast</td><td>Y</td><td>N</td><td>de Jong et al., 2007</td></tr><tr><td>1998</td><td>–</td><td>Pacific</td><td>–</td><td>Y</td><td>N</td><td>Obata et al., 2007</td></tr><tr><td>2001</td><td>3–5</td><td>Pacific</td><td>Northwest</td><td>N</td><td>N</td><td>Johnson et al., 2003</td></tr><tr><td>2002</td><td>10</td><td>Atlantic</td><td>Northeast</td><td>Y</td><td>N</td><td>Kramer et al., 2004</td></tr><tr><td>2003</td><td>6–8</td><td>Atlantic</td><td>Latitudinal</td><td>Y</td><td>N</td><td>Measures et al., 2008a</td></tr><tr><td>2004</td><td>2, 3</td><td>Southern</td><td>Atlantic sector</td><td>Y</td><td>N</td><td>Measures et al., 2013</td></tr><tr><td>2004</td><td>1</td><td>Pacific</td><td>Equatorial</td><td>Y</td><td>N</td><td>Kaupp et al., 2011</td></tr><tr><td>2005</td><td>10, 11</td><td>Atlantic</td><td>East</td><td>N</td><td>N</td><td>Pohl et al., 2011</td></tr><tr><td>2005</td><td>8, 9</td><td>Pacific</td><td>North</td><td>Y</td><td>Y</td><td>Zheng et al., 2019</td></tr><tr><td>2006</td><td>8, 9</td><td>Pacific</td><td>Equatorial</td><td>Y</td><td>N</td><td>Slemons et al., 2010</td></tr><tr><td>2007</td><td>1, 2</td><td>Southern</td><td>Tasman Sea</td><td>Y</td><td>Y</td><td>Remenyi, 2013</td></tr><tr><td>2007</td><td>–</td><td>Atlantic</td><td>Northeast</td><td>Y</td><td>Y</td><td>Middag test</td></tr><tr><td>2007</td><td>7–9</td><td>Arctic</td><td>–</td><td>Y</td><td>Y</td><td>Middag et al., 2009</td></tr><tr><td>2007</td><td>2, 3</td><td>Indian</td><td>South</td><td>Y</td><td>N</td><td>Grand et al., 2015a</td></tr><tr><td>2007</td><td>4</td><td>Indian</td><td>North</td><td>Y</td><td>N</td><td>Grand et al., 2015a</td></tr><tr><td>2008</td><td>3</td><td>Southern</td><td>Atlantic sector</td><td>Y</td><td>Y</td><td>Middag et al., 2011</td></tr><tr><td>2008</td><td>3</td><td>Southern</td><td>Atlantic sector</td><td>Y</td><td>Y</td><td>Middag et al., 2012</td></tr><tr><td>2008</td><td>3, 4</td><td>Southern</td><td>Australian sector</td><td>Y</td><td>Y</td><td>Remenyi, 2013</td></tr><tr><td>2008</td><td>2, 3</td><td>Southern</td><td>Atlantic sector</td><td>Y</td><td>Y</td><td>Croot unpublished</td></tr><tr><td>2008</td><td>2, 3</td><td>Southern</td><td>Indian sector</td><td>Y</td><td>N</td><td>Grand et al., 2015b</td></tr><tr><td>2009</td><td>3–5</td><td>Indian</td><td>Longitudinal</td><td>Y</td><td>N</td><td>Grand et al., 2015b</td></tr><tr><td>2009</td><td>11, 12</td><td>Indian</td><td>Latitudinal</td><td>Y</td><td>Y</td><td>Thi Dieu Vu and Sohrin, 2013</td></tr><tr><td>2009</td><td>11, 12</td><td>Atlantic</td><td>Tropical</td><td>Y</td><td>Y</td><td>Dammshäuser et al., 2013</td></tr><tr><td>2010</td><td>4, 5</td><td>Atlantic</td><td>Northwest</td><td>Y</td><td>Y</td><td>Middag et al., 2015</td></tr><tr><td>2010</td><td>6, 7</td><td>Atlantic</td><td>Northwest</td><td>Y</td><td>Y</td><td>Middag et al., 2015</td></tr><tr><td>2010</td><td>10, 11</td><td>Atlantic</td><td>Tropical</td><td>Y</td><td>N</td><td>Measures et al., 2015</td></tr><tr><td>2010</td><td>4, 5</td><td>Atlantic</td><td>North</td><td>Y</td><td>Y</td><td>Klar unpublished</td></tr><tr><td>2010</td><td>5</td><td>Atlantic</td><td>North</td><td>Y</td><td>Y</td><td>Klar unpublished</td></tr><tr><td>2010</td><td>7, 8</td><td>Atlantic</td><td>North</td><td>Y</td><td>Y</td><td>Klar unpublished</td></tr><tr><td>2010</td><td>4, 5</td><td>Atlantic</td><td>Latitudinal</td><td>Y</td><td>Y</td><td>Dammshäuser et al., 2013</td></tr><tr><td>2010</td><td>4, 5</td><td>Atlantic</td><td>Latitudinal</td><td>Y</td><td>Y</td><td>Dammshauser et al., 2011</td></tr><tr><td>2011</td><td>5, 6</td><td>Pacific</td><td>West</td><td>Y</td><td>Y</td><td>Bowie unpublished</td></tr><tr><td>2011</td><td>1</td><td>Atlantic</td><td>South</td><td>Y</td><td>Y</td><td>Klar unpublished</td></tr><tr><td>2011</td><td>3, 4</td><td>Atlantic</td><td>Southwest</td><td>Y</td><td>Y</td><td>Middag et al., 2015</td></tr><tr><td>2011</td><td>2, 3</td><td>Atlantic</td><td>Tropical</td><td>Y</td><td>Y</td><td>Klar unpublished</td></tr><tr><td>2011</td><td>2, 3</td><td>Atlantic</td><td>Tropical</td><td>Y</td><td>Y</td><td>Schlosser et al., 2014</td></tr><tr><td>2011</td><td>7</td><td>Pacific</td><td>North</td><td>Y</td><td>Y</td><td>Zheng et al., 2019</td></tr><tr><td>2012</td><td>8, 9</td><td>Pacific</td><td>North</td><td>Y</td><td>Y</td><td>Zheng et al., 2019</td></tr><tr><td>2012</td><td>8</td><td>Atlantic</td><td>Northwest</td><td>Y</td><td>Y</td><td>Middag et al., 2015</td></tr><tr><td>2013</td><td>8–10</td><td>Atlantic</td><td>Latitudinal</td><td>Y</td><td>Y</td><td>Barrett et al., 2015</td></tr><tr><td>2013</td><td>10–12</td><td>Pacific</td><td>South</td><td>Y</td><td>Y</td><td>Resing et al., 2015</td></tr><tr><td>2013</td><td>5, 6</td><td>Mediterranean</td><td>–</td><td>Y</td><td>Y</td><td>Rolison et al., 2015</td></tr><tr><td>2013</td><td>7, 8</td><td>Mediterranean</td><td>Black Sea</td><td>Y</td><td>Y</td><td>Rolison et al., 2015</td></tr><tr><td>2014</td><td>5, 6</td><td>Atlantic</td><td>North</td><td>Y</td><td>Y</td><td>Menzel Barraqueta et al., 2018</td></tr><tr><td>2014</td><td>6</td><td>Atlantic</td><td>Mauritania shelf</td><td>Y</td><td>Y</td><td>Rapp et al., 2019</td></tr></tbody></table>

(Continued)
<table><caption>TABLE 1 | Continued</caption><thead><tr><th>Sampling year</th><th>Month</th><th>Ocean/Sea</th><th>Region</th><th>Filter (Yes/No)</th><th>Reference material</th><th>References</th></tr></thead><tbody><tr><td>2015</td><td>11, 12</td><td>Atlantic</td><td>Southeast</td><td>Y</td><td>Y</td><td>Menzel Barraqueta unpublished</td></tr><tr><td>2015</td><td>5</td><td>Pacific</td><td>Southwest</td><td>Y</td><td>Y</td><td>Middag unpublished</td></tr><tr><td>2016</td><td>5</td><td>Pacific</td><td>Southwest</td><td>Y</td><td>Y</td><td>Middag unpublished</td></tr><tr><td>2016</td><td>3, 4</td><td>Indian</td><td>Tropical</td><td>Y</td><td>Y</td><td>Singh et al., 2020</td></tr><tr><td>2017</td><td>1–3</td><td>Indian</td><td>BoB</td><td>Y</td><td>Y</td><td>Singh et al., 2020</td></tr></tbody></table>

Data not included in the database (reference). Kaupp et al. (2011) (Surface data in the database); Li et al. (2013), Liu et al. (2017), Measures et al. (1986), Measures et al. (2005), Measures and Edmond (1992), Ren et al. (2006), Ren et al. (2011), Vink et al. (2000). Month refers to the month of sampling being 1 and 12 January and December, respectively. Information not available in the manuscript is noted with an interrupted dash line. Yes and No are denoted as Y and N, respectively. Region sampled refers to the location where the majority of sampling took place.

<figure><img src="image_3.png" /></figure>

dAl concentration data statistics and representative dAl depth profiles; (iii) assessment of data variability over time.

The different regions and geographical boundaries analyzed below are: Atlantic Ocean (60 °N to 60 °S), North Atlantic

(NATL, 60 °N to 30 °N), tropical Atlantic (TATL, 30 °N to 30 °S), South Atlantic (SATL, 30° to 60° S), Pacific Ocean (PAC, 60 °N to 60 °S), Indian Ocean (IND, 10 °N to 60 °S), Southern Ocean (SO, south of 60 °S), Arabian Sea (ARS, > 10 °N), Mediterranean
Sea (MED, east of 7 °E), and Arctic Ocean (ARC, north of 60 °N). The non-differentiation between northern and southern regions in the Pacific Ocean and Indian oceans arises from a lack of dAl data. The division of the Atlantic Ocean tries to capture the large differences in dAl concentrations between the northern, southern and tropical regions.

## Glimpse Into Sampling Efforts

The Al dataset shows an uneven coverage in sampling between different regions, different seasons, and depths in the water column. Geographically, half of the data points correspond to the Atlantic Ocean (48%), followed by the Pacific and Indian Oceans (18 and 11%, respectively). The Mediterranean Sea and the Southern Ocean account for 6 and 7% of the total dAl data, while the Arctic Ocean represents just 3% of the total data. From a historical point of view, a sharp rise in total seawater dAl concentration data is observed on a decadal timescale with 69% of the total data collected after the year 2000 (Figure 1). The increase in basin scale knowledge of dAl biogeochemistry arises from the GEOTRACES programme, and other recent smaller scale research programmes. For example, 83 and 50% of dAl concentration data for the Mediterranean Sea and Atlantic Ocean were collected in the last 7 years of the database (2010 to 2017). In contrast, the Arctic and Southern Oceans have not seen any new data during the same period (2010 to 2017). During the last decade (2000 to 2009) and thanks to the International Polar Year cruises the number of samples collected in the two previously mentioned ocean basins increased by 91 and 68%, respectively. Nearly 71% of the expeditions have taken place in the northern hemisphere which was thus sampled more often than the southern hemisphere (63 vs. 37%). From a seasonal point of view, with 61 and 64% of the total expeditions for the northern and southern hemisphere, respectively, most of the sampling was conducted during spring and summer months (Table 1). However, nearly no data exists in austral winter for the Southern Ocean. Within the water column, 21% of the sampling points correspond to the first 20 m, 43% to the upper 100 m, 26% to a depth between 100 and 500 m, and 33% to a depth below 500 m. A special case is seen in the Indian Ocean where observations below 1,000 m are limited to only 372 samples.

## Global Dissolved Al Concentrations Data Statistics

Table 2 shows global mean, median, minimum and maximum dAl concentration data for the different oceanic regions. Globally, the mean and median oceanic concentrations of dAl are 15.4 ± 25.9 and 6.8 nM (n = 24,194), respectively. Maximum and minimum Al concentrations were 674 nM (Arabian Sea) and 0.05 nM (Southern Ocean), respectively. It is noticeable that there is a large amount of data (n = 590) with concentrations over 100 nM which correspond to regions that are strongly influenced by Al sources (e.g., atmospheric, hydrothermal, riverine, and sedimentary). The mean dAl concentration includes data points (2.4%) directly affected by sources of Al, therefore the median value may represent a better estimate. In the following, samples with concentrations above 300 nM are not considered. Highest mean and median concentrations are found in the Mediterranean

Sea (91.1 ± 42.6 and 85.3 nM) followed by the Arabian Sea (16.7 ± 37 and 7.8) and the Atlantic Ocean (16.3 ± 12.5 and 13.9 nM). Lowest mean and median Al concentration data are found in the Southern Ocean (1.7 ± 20.6 and 0.5 nM) followed by the Pacific (3.1 ± 3.1 and 2.3 nM), Indian (4.1 ± 3.7 and 3.3), and Arctic (8.4 ± 7.9 and 4.9 nM) Oceans. In surface waters (0–100 m) highest mean Al concentrations are observed in the Mediterranean Sea (54.9 ± 22.9 nM, n = 375) followed by the Arabian Sea (20 ± 45.3, n=970), and the Atlantic (19.8 ± 15.8 nM, n = 4,747), Indian (5.5 ± 5.5 nM, n = 882), Pacific (3.3 ± 3.5 nM, n = 2,118), Arctic (2.7 ± 3.4 nM, n = 234) and Southern (0.8 ± 0.9 nM, n = 714) Oceans. In intermediate waters (500–2,000 m) highest mean Al concentrations are observed in the Mediterranean Sea (127 ± 29 nM, n = 321) followed by the Arabian Sea (25.7 ± 12.6, n = 58), and the Atlantic (13.1 ± 8 nM, n = 2,673), Arctic (6 ± 2.3, n = 76), Indian (3.1 ± 1 nM, n = 600), Pacific (2 ± 1.7 nM, n = 678), and Southern (0.7 ± 0.7 nM, n = 273) Oceans. In deep waters (2,000 m to bottom) the same trend is noticeable with highest mean Al concentrations observed in the Mediterranean Sea (118 ± 53.3 nM, n = 236) followed by the Arabian Sea (28.8 ± 7.7, n = 7), and the Atlantic (17.6 ± 8.7 nM, n = 1,790), Arctic (12.3 ± 4.4 nM, n = 106), Pacific (3.1 ± 2.6 nM, n = 674), Indian (2.5 ± 0.9 nM, n = 148), and Southern (0.9 ± 0.6 nM, n = 196) Oceans. To provide a more useful surface water Al estimate we extracted the depth of the surface mixed layer (SML) for the regions of interest from a monthly mixed layer climatology calculated using the density threshold method (density criterion of 0.03 kg m⁻³, Holte et al., 2017. In the SML highest mean Al concentrations are observed in the Mediterranean Sea (55.3 ± 43) followed by the Arabian Sea (23.3 ± 37.3), and the Atlantic (21.6 ± 16.1 nM), Indian (6.2 ± 6.3 nM), Pacific (3.2 ± 3.4 nM), Arctic (3 ± 7.9), and Southern (0.8 ± 0.9 nM) Oceans.

## "Representative" Al Depth Profiles

With the aim to provide representative dAl depth profiles for major oceanic regions we have further constrained the available Al data. To avoid profiles affected by continental inputs, we have selected only off-shelf samples, which we define as being located at least 50 nautical miles offshore. Large intra and inter-basin differences in the shape of mean Al depth profiles are evident (Figure 1) with varying dAl distributions displaying either a nutrient, scavenged, or mixed-type profile. This reveals that Al is a highly dynamic metal with different responses to different oceanographic settings and therefore is a useful indicator for processes (e.g., input and removal of metals) occurring in the marine environment.

## Data Variability Over Time

Whether dAl data variability over time can be attributed to improvements in sampling and analytical techniques is difficult to assess and relies on large assumptions that may not be correct (e.g., comparable seasonal and geographical coverage in sampling). The choice of a cut-off year between historical and recent observations is complicated. In this attempt to assess data variability over time we have chosen the year 2002
<table><caption>TABLE 2 | Main global Al concentration data (nM) statistics.</caption><thead><tr><th>Ocean or sea</th><th>Mean</th><th>Median</th><th>Minimum</th><th>Maximum</th><th>MLD</th><th>Surface (0-100)</th><th>Sub-surface (100-500)</th><th>Mid (500-2,000)</th><th>Deep (2,000-bottom)</th></tr></thead><tbody><tr><td>All data</td><td>15.4 ± 25.9</td><td>6.8</td><td>0.05</td><td>673.4</td><td>-</td><td>14.7 ± 22.9</td><td>13.2 ± 22</td><td>16.8 ± 31.3</td><td>20.1 ± 32.3</td></tr><tr><td>n = 24,194</td><td></td><td></td><td></td><td></td><td></td><td>n = 10,252</td><td>n = 6,379</td><td>n = 4,896</td><td>n = 3,261</td></tr><tr><td>Atlantic O.</td><td>16.3 ± 12.5</td><td>13.9</td><td>0.1</td><td>313.7</td><td>21.6 ± 16.1</td><td>19.8 ± 15.6</td><td>12.2 ± 9.6</td><td>13.1 ± 8</td><td>17.6 ± 8.7</td></tr><tr><td>n = 11,624</td><td></td><td></td><td></td><td></td><td>z = 65</td><td>n = 4,747</td><td>n = 2,642</td><td>n = 2,673</td><td>n = 1,790</td></tr><tr><td>NATL</td><td>16.4 ± 9.4</td><td>15.4</td><td>0.44</td><td>64.5</td><td>12.8 ± 10.9</td><td>12.7 ± 10.7</td><td>14.8 ± 9.4</td><td>17.2 ± 7.5</td><td>22.1 ± 6.2</td></tr><tr><td>n = 4,309</td><td></td><td></td><td></td><td></td><td>z = 91</td><td>n = 1,214</td><td>n = 1,031</td><td>n = 1,342</td><td>n = 845</td></tr><tr><td>TATL</td><td>19.8 ± 13.9</td><td>16.2</td><td>0.16</td><td>313.7</td><td>27.4 ± 15.7</td><td>25 ± 15.6</td><td>13.5 ± 9.4</td><td>11.3 ± 5.6</td><td>17.8 ± 7.3</td></tr><tr><td>n = 5,662</td><td></td><td></td><td></td><td></td><td>z = 49</td><td>n = 3,083</td><td>n = 1,153</td><td>n = 889</td><td>n = 617</td></tr><tr><td>SATL</td><td>3.7 ± 4.3</td><td>2.2</td><td>0.1</td><td>50</td><td>4.9 ± 6.4</td><td>4.8 ± 6</td><td>3.2 ± 3.2</td><td>2.7 ± 2.2</td><td>4.6 ± 3.4</td></tr><tr><td>n = 1,241</td><td></td><td></td><td></td><td></td><td>z = 77</td><td>n = 344</td><td>n = 311</td><td>n = 299</td><td>n = 292</td></tr><tr><td>Arabian Sea</td><td>16.7 ± 37</td><td>7.8</td><td>0.2</td><td>673.4</td><td>23.3 ± 37.3</td><td>20 ± 45.3</td><td>9.5 ± 6.9</td><td>25.7 ± 12.6</td><td>28.8 ± 7.7</td></tr><tr><td>n = 1,511</td><td></td><td></td><td></td><td></td><td>z = 39</td><td>n = 970</td><td>n = 505</td><td>n = 58</td><td>n = 7</td></tr><tr><td>Arctic O.</td><td>8.4 ± 7.9</td><td>4.9</td><td>0.29</td><td>28.19</td><td>3 ± 7.9</td><td>2.7 ± 3.4</td><td>3.1 ± 1.6</td><td>6 ± 2.3</td><td>12.3 ± 4.4</td></tr><tr><td>n = 734</td><td></td><td></td><td></td><td></td><td>z = 60</td><td>n = 234</td><td>n = 165</td><td>n = 76</td><td>n = 106</td></tr><tr><td>Black S.</td><td>4 ± 5.4</td><td>3.1</td><td>52.8</td><td>0.6</td><td>11.6 ± 5.4</td><td>6.2 ± 9.1</td><td>3.7 ± 0.8</td><td>2.6 ± 0.8</td><td>1.9 ± 1</td></tr><tr><td>n = 251</td><td></td><td></td><td></td><td></td><td>z = 21</td><td>n = 80</td><td>n = 106</td><td>n = 29</td><td>n = 40</td></tr><tr><td>Indian O.</td><td>4.1 ± 3.7</td><td>3.3</td><td>0.3</td><td>51.2</td><td>6.2 ± 6.3</td><td>5.5 ± 5.5</td><td>3.7 ± 2.1</td><td>3 ± 1</td><td>2.5 ± 0.9</td></tr><tr><td>n = 2,573</td><td></td><td></td><td></td><td></td><td>z = 64</td><td>n = 882</td><td>n = 1,006</td><td>n = 600</td><td>n = 148</td></tr><tr><td>Mediterranean S.</td><td>91.1 ± 42.6</td><td>85.3</td><td>10.3</td><td>178.1</td><td>55.3 ± 43</td><td>54.9 ± 22.9</td><td>81.7 ± 25.9</td><td>127.7 ± 29</td><td>118 ± 53.3</td></tr><tr><td>n = 1,338</td><td></td><td></td><td></td><td></td><td>z = 42</td><td>n = 375</td><td>n = 468</td><td>n = 321</td><td>n = 236</td></tr><tr><td>Pacific O.</td><td>3.1 ± 3.1</td><td>2.3</td><td>0.05</td><td>33.7</td><td>3.2 ± 3.4</td><td>3.3 ± 3.5</td><td>3.5 ± 3.2</td><td>2 ± 1.7</td><td>3.1 ± 2.6</td></tr><tr><td>n = 4,240</td><td></td><td></td><td></td><td></td><td>z = 61</td><td>n = 2,118</td><td>n = 906</td><td>n = 678</td><td>n = 674</td></tr><tr><td>Southern O.</td><td>1.7 ± 20.6</td><td>0.5</td><td>0.07</td><td>660.2</td><td>0.8 ± 0.9*</td><td>0.8 ± 0.9*</td><td>0.8 ± 0.9</td><td>0.7 ± 0.7</td><td>0.9 ± 0.6</td></tr><tr><td>n = 1,669</td><td></td><td></td><td></td><td></td><td>z = 61</td><td>n = 714</td><td>n = 512</td><td>n = 273</td><td>n = 196</td></tr><tr><th>Variability over time</th><th>Atlantic</th><th>Pacific</th><th>Mediterranean</th><th>Indian</th><th>SO</th><th>NATL</th><th>TATL</th><th>SATL</th></tr><tr><td>&lt;year 2002</td><td>23.3 ± 13.7<br>(n = 4,443)</td><td>2.8 ± 2.7<br>(n = 1,757)</td><td>93.6 ± 49<br>(n = 285)</td><td>5.7 ± 3.7<br>(n = 182)</td><td>2.7 ± 33<br>(n = 651)</td><td>19 ± 9.1<br>(n = 2,060)</td><td>27.8 ± 15.3<br>(n = 2,289)</td><td>7.8 ± 8.3<br>(n = 87)</td></tr><tr><td>≥year 2002</td><td>11.9 ± 9.4<br>(n = 7,181)</td><td>3.4 ± 3.3<br>(n = 2,483)</td><td>90.5 ± 40.7<br>(n = 1,053)</td><td>4 ± 3.6<br>(n = 2,392)</td><td>1 ± 0.8<br>(n = 1,018)</td><td>13.9 ± 8.9<br>(n = 2,249)</td><td>14.3 ± 9.5<br>(n = 3,373)</td><td>3.4 ± 3.6<br>(n = 1,154)</td></tr><tr><td>P-value (α = 0.001)</td><td>&lt;0.0000</td><td>&lt;0.0000</td><td>0.2576</td><td>&lt;0.0000</td><td>&lt;0.0000</td><td>&lt;0.0000</td><td>&lt;0.0000</td><td>&lt;0.0000</td></tr><tr><td>H₀</td><td>Rejected</td><td>Rejected</td><td>Accepted</td><td>Rejected</td><td>Rejected</td><td>Rejected</td><td>Rejected</td><td>Rejected</td></tr><tr><td>&lt; year 2002</td><td>19.7 ± 7.3<br>(n = 1,364)</td><td>2.4 ± 2.0<br>(n = 214)</td><td>104.1 ± 59<br>(n = 285)</td><td>26.3 ± 11.2<br>(n = 36)</td><td>0.6 ± 0.6<br>(n = 160)</td><td>20.7 ± 6.8<br>(n = 1,116)</td><td>16.6 ± 7.2<br>(n = 219)</td><td>6.8 ± 5.7<br>(n = 22)</td></tr><tr><td>≥ year 2002</td><td>13.6 ± 7.9<br>(n = 2,833)</td><td>2.9 ± 2.2<br>(n = 982)</td><td>131.3 ± 26<br>(n = 380)</td><td>3.1 ± 1.2<br>(n = 789)</td><td>0.9 ± 0.7<br>(n = 302)</td><td>17.5 ± 7.7<br>(n = 1,035)</td><td>13.5 ± 6.9<br>(n = 1,285)</td><td>4.2 ± 2.7<br>(n = 345)</td></tr><tr><td>P-value (α = 0.001)</td><td>&lt;0.0000</td><td>&lt;0.0000</td><td>0.0361</td><td>&lt;0.0000</td><td>&lt;0.0000</td><td>0.0000</td><td>&lt;0.0000</td><td>0.0444</td></tr><tr><td>H₀</td><td>Rejected</td><td>Rejected</td><td>Accepted</td><td>Rejected</td><td>Rejected</td><td>Rejected</td><td>Rejected</td><td>Accepted</td></tr></tbody></table>

SO, Southern Ocean; NATL, North Atlantic Ocean; TATL, Tropical Atlantic Ocean; and SATL, South Atlantic Ocean. The statistics marked with a star do not consider samples with values above 300 nM (n = 3). The depth interval statistics shows average and standard deviation. The mid and deep depth interval for the Arctic is 500–1,000 and 1,000–2,000 m, respectively. Hypothesis 0 (H₀) refers to no statistically significant difference between samples collected prior and after the year 2000. MLD refers to Mixed Layer Depth. The MLD depth has been extracted for the regions of interest from the monthly mixed layer climatology calculated using the density threshold method (Holte et al., 2017).
which coincided with the advent of large-scale clean seawater
sampling capabilities (De Baar et al., 2008; Measures et al.,
2008b). We have investigated the Atlantic (including the three
Atlantic regions defined in the above section), Indian (excluding
the Arabian Sea), Pacific, and Southern Oceans as well as
the Mediterranean Sea and include analysis for all data as
well as for values below 500 m depth (to reduce the influence
of seasonal variability in an element with short residence
times). A graphical representation on the location of data
for both analysis is shown in the **Supplementary Figures 1, 2**.
We acknowledge that no differentiation is made between
analytical methods and that some datasets may be directly
influenced by Al sources. However, we assume improvements
in analytical and sampling techniques in recent decades and
we consider that both datasets (before the year 2002 and
after) will contain regions where samples directly influenced
by strong Al sources were collected. To assess if Al data have
varied over time for the same oceanic regions, we applied
the two tailed non-parametric Mann-Whitney test (including
outliers) which shows the probability that a randomly chosen
group (e.g., A or B) is statistically different to the other group.
The test rejected the H₀ hypothesis (A = B) at a significant
level α < 0.001 for all analysis except for the Mediterranean
Sea in both analysis (all data and below 500 m, **Table 2**). An
exception is the South Atlantic Ocean where H₀ is accepted
when considering data below 500 m. Although it is noticeable
that Al data below 500 meters for the South Atlantic Ocean
before the year 2002 are restricted to only two stations and
22 data points (**Supplementary Figure 2** and **Table 2**). This
indicates that the distribution of independent observations from
both groups (prior to 2002 and onwards) are significantly
different for all major oceans except for the Mediterranean
Sea and the South Atlantic Ocean when considering only
data below 500 m. The reason for no significant difference for
the Mediterranean Sea could be to the high concentrations
found in this region (**Table 2**), making any influence of
improvements in analytical and sampling techniques for trace
constituents negligible. Although an effect of improved analytical
and sampling techniques seems likely based on the observed
difference between historical and recent observations, this
observation is by no means conclusive evidence. Therefore, the
influence of spatial coverage needs to be considered. Ideally, in
order to provide better evidence relating lower Al concentrations
with improvement in sampling and analytical techniques we
would require repeated sampling in the same region over long
periods of time.

SUMMARY AND PROSPECTS

We have compiled 24,194 dAl concentration data points for
the global ocean spanning a sampling period from 1973 to
2017. We further provided global dAl concentration statistics for
each of the major oceanic, enclosed, and semi-enclosed basins
and provided global average depth profiles for representative
areas within the major regions. The compilation shows a large
variability in dAl concentration data which highlights the varying

magnitude of input and removal rates. It also highlights our
limited knowledge on how dAl varies between seasons and the
relative lack of observations in regions such as the Pacific and
Indian Oceans. This opens interesting research questions to
plan future research expeditions. For example, an interesting
region for research is the western Indian Ocean. Here the
role of the southwards flowing western boundary currents as a
carrier of Al (and other trace metals) to the Southwest Indian
subtropical gyre via the Mozambique Channel has been suggested
(Grand et al., 2015a) but requires additional studies to highlight
the extent of this supply and the influence that Mozambique
eddies embedded in the Agulhas Current could have further
south. This area would also produce new knowledge on the
continent-island influence on trace metal distributions in a highly
dynamic area. Another interesting area is the western Pacific
along the American continent where the influence of upwelling
on the distribution of Al remains less well-constrained than, for
example, for the upwelling regions along the western African
continent. We believe that the Al compilation will be a useful
tool for modeling purposes and will help to better understand
the global biogeochemical cycle of Al. Combined with global
data products on mixed layer depths the Al data compilation
can be used to revise residence times of Al in surface waters as
well as updating the global oceanic Al inventory. Furthermore,
an additional combination with global chlorophyll data products
could investigate the role that biogenic particles (e.g., assuming
the more chlorophyll the more particles present in surface waters)
may have on the residence times of Al in surface waters and
elucidate if chlorophyll global products could be used to better
constrain Al residence times in surface waters.

DATA AVAILABILITY STATEMENT

The data compiled in this study have been deposited in an open
access repository and is available under the following link https://
doi.org/10.25413/sun.12167877.v1.

AUTHOR CONTRIBUTIONS

J-LM conceived the study, wrote the manuscript with early
contributions from AR, and compiled the database. TD, RC, JL,
and SS helped with data compilation. EA, JK, RM, AB, PC, TR,
and MG-C submitted unpublished data. AR provided funds for
the study. All co-authors commented on previous manuscript
drafts and on the final manuscript draft. All authors contributed
to the article and approved the submitted version.

FUNDING

This study was funded by NRF, South Africa (UID# 105826 AND
110715).

ACKNOWLEDGMENTS

We would like to extend our gratitude to all scientists and
personnel involved in the collection and analysis of all the
samples included in the database. Special thanks to Marco Van Hulten and Marion Gehlen for providing their early aluminum compilations. Also, special thanks to all researchers who provided, upon request, their Al data. This study was funded by NRF, South Africa (UID# 105826 AND 110715).

## SUPPLEMENTARY MATERIAL

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fmars.2020.00468/full#supplementary-material

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**Conflict of Interest:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The reviewer MG declared a past co-authorship with several of the authors EA, AB, and RM to the handling editor.

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