Manganese biogeochemistry in the sunlit ocean = Die Biogeochemie des Mangans in der euphotischen Zone

The trace metal manganese (Mn) plays a significant role in seawater as it is bio-essential for phytoplankton. Mn plays a critical role as a redox center in Photosystem II (PSII) during the conversion of water to oxygen in photosynthesis. It is also essential in other redox related enzymatic processes; in particular Mn is important as the active metal center in superoxide dismutase (SOD) which provides intracellular protection against oxidative stress due to photochemically produced superoxide (O2 ). Mn exists in seawater in three redox states: soluble and prevalent Mn(II), insoluble Mn(III) and Mn(IV)-oxides. In the euphotic zone the biogeochemical cycling of Mn is strongly influenced by reactive oxygen species (ROS). The highly reactive and short-lived superoxide (O2 ) and hydrogen peroxide (H2O2) can both act as oxidants and reductants, and they play a key role in the Mn processes in seawater. For example the dominant Mn sources to the open ocean are the Mn-oxides which are present in atmospheric dust which are reduced to soluble Mn(II) by photochemically produced H2O2. While these processes have been crudely identified, the dominant reactions and mechanisms of Mn and ROS in seawater are poorly understood. This lack of knowledge demands investigations into the in-situ dissolution processes of Mn from dust and into studying the exact reaction mechanisms between Mn and ROS in the euphotic zone. This thesis comprises four manuscripts. Manuscripts 1 and 2 (Wuttig et al., subm., 2013a; Wuttig et al., subm., 2013b) focus on the cycling and reaction mechanisms of Mn and ROS. Manuscript 3 (Wuttig et al., in prep., 2013) addresses differences in the input and distribution of cadmium (Cd), iron (Fe) and Mn in the Eastern Tropical Atlantic Ocean off Cape Verde, and manuscript 4 (Wuttig et al., 2013) describes Mn cycling after dust additions in a trace metal clean mesocosm experiment in the Mediterranean Sea. This study has conclusively shown that Mn and organic matter are the dominant sinks for O2 in the Eastern Tropical North Atlantic (manuscripts 1; Wuttig et al., subm., 2013a). Mn dominates this decay especially in the surface waters which are influenced by high atmospheric dust deposition and near the sediment/water interface due to Mn sediment resuspension. This contrasts with current knowledge based on findings from the Mn poor Southern Ocean where copper (Cu) was shown to be the major sink. In manuscript 2 it is demonstrated that O2 decays by reaction with inorganic Mn(II) in seawater following a first order loss rate which appears to involve a catalytic reaction involving the Mn(II)/MnO2+ couple, in which MnO2+ is a manganous superoxide complex (Wuttig et al., subm., 2013a). Thus in sunlit and oxygenated waters Mn(III) is unlikely to be found in significant concentrations when strong Mn(III) binding ligands are not present. In other studies Mn(III) was found under anoxic conditions in the presence of unknown strong Mn(III) binding ligands. Therefore, in contrast to the Mn(II)/MnO2+ pair, Mn(III) cannot act as a SOD in the oxygenated surface ocean. In the Eastern Tropical North Atlantic Ocean atmospheric dust is the main source of Mn to surface waters (manuscript 3; Wuttig et al., in prep., 2013). However this study provides clear evidence that equatorial upwelling and sediment resuspension are important Mn sources in this region. In contrast to findings from the Eastern Tropical Pacific, where unexpected high surface concentrations were observed, no secondary Mn(II) maximum was found in the Eastern Tropical North Atlantic Ocean. This could have been introduced by a combination of lateral transport of Mn rich waters from the coastal margins and reduction of Mn-oxides. While Aeolian sources were predominantly influencing Mn and also Fe cycling in the Eastern Tropical Atlantic, Cd was not controlled by dust deposition (manuscript 3; Wuttig et al., in prep., 2013). These biologically relevant elements exhibited contrasting distribution patterns. For Fe and Mn, atmospheric depositions masked a classical nutrient type profile, while Cd was very depleted at the surface and concentrations steadily increased with depth. Cd was highly correlated to Phosphate (hereafter referred to as P). The Cd/P ratio was mainly controlled by P with elevated concentrations at depth resulting in strongly differing ratios in surface and subsurface layers of 16.6 pmol / µmol and 237 pmol / µmol, respectively. The complex photochemical processes during the dissolution of Mn dust are also subject of manuscript 4. This paper describes a mesocosm project in the Mediterranean with two consecutive additions of evapocondensed dust conducted. The data also show that the dissolution and loss rates of Mn were comparable during both seedings. The calculated fractional solubilities for the first and the second dust addition were 41 ± 9 % and 27 ± 19 %, respectively. The results presented in this thesis have significantly improved our understanding of Mn distribution and especially cycling in the euphotic zone. An insight into the mechanisms between Mn and ROS and into the dissolution processes from dust is given

Die Biogeochemie des Mangans in der euphotischen Zone

The trace metal manganese (Mn) plays a significant role in seawater as it is bio-essential for phytoplankton. Mn plays a critical role as a redox center in Photosystem II (PSII) during the conversion of water to oxygen in photosynthesis. It is also essential in other redox related enzymatic processes; in particular Mn is important as the active metal center in superoxide dismutase (SOD) which provides intracellular protection against oxidative stress due to photochemically produced superoxide (O2 ). Mn exists in seawater in three redox states: soluble and prevalent Mn(II), insoluble Mn(III) and Mn(IV)-oxides. In the euphotic zone the biogeochemical cycling of Mn is strongly influenced by reactive oxygen species (ROS). The highly reactive and short-lived superoxide (O2 ) and hydrogen peroxide (H2O2) can both act as oxidants and reductants, and they play a key role in the Mn processes in seawater. For example the dominant Mn sources to the open ocean are the Mn-oxides which are present in atmospheric dust which are reduced to soluble Mn(II) by photochemically produced H2O2. While these processes have been crudely identified, the dominant reactions and mechanisms of Mn and ROS in seawater are poorly understood. This lack of knowledge demands investigations into the in-situ dissolution processes of Mn from dust and into studying the exact reaction mechanisms between Mn and ROS in the euphotic zone. This thesis comprises four manuscripts. Manuscripts 1 and 2 (Wuttig et al., subm., 2013a; Wuttig et al., subm., 2013b) focus on the cycling and reaction mechanisms of Mn and ROS. Manuscript 3 (Wuttig et al., in prep., 2013) addresses differences in the input and distribution of cadmium (Cd), iron (Fe) and Mn in the Eastern Tropical Atlantic Ocean off Cape Verde, and manuscript 4 (Wuttig et al., 2013) describes Mn cycling after dust additions in a trace metal clean mesocosm experiment in the Mediterranean Sea. This study has conclusively shown that Mn and organic matter are the dominant sinks for O2 in the Eastern Tropical North Atlantic (manuscripts 1; Wuttig et al., subm., 2013a). Mn dominates this decay especially in the surface waters which are influenced by high atmospheric dust deposition and near the sediment/water interface due to Mn sediment resuspension. This contrasts with current knowledge based on findings from the Mn poor Southern Ocean where copper (Cu) was shown to be the major sink. In manuscript 2 it is demonstrated that O2 decays by reaction with inorganic Mn(II) in seawater following a first order loss rate which appears to involve a catalytic reaction involving the Mn(II)/MnO2+ couple, in which MnO2+ is a manganous superoxide complex (Wuttig et al., subm., 2013a). Thus in sunlit and oxygenated waters Mn(III) is unlikely to be found in significant concentrations when strong Mn(III) binding ligands are not present. In other studies Mn(III) was found under anoxic conditions in the presence of unknown strong Mn(III) binding ligands. Therefore, in contrast to the Mn(II)/MnO2+ pair, Mn(III) cannot act as a SOD in the oxygenated surface ocean. In the Eastern Tropical North Atlantic Ocean atmospheric dust is the main source of Mn to surface waters (manuscript 3; Wuttig et al., in prep., 2013). However this study provides clear evidence that equatorial upwelling and sediment resuspension are important Mn sources in this region. In contrast to findings from the Eastern Tropical Pacific, where unexpected high surface concentrations were observed, no secondary Mn(II) maximum was found in the Eastern Tropical North Atlantic Ocean. This could have been introduced by a combination of lateral transport of Mn rich waters from the coastal margins and reduction of Mn-oxides. While Aeolian sources were predominantly influencing Mn and also Fe cycling in the Eastern Tropical Atlantic, Cd was not controlled by dust deposition (manuscript 3; Wuttig et al., in prep., 2013). These biologically relevant elements exhibited contrasting distribution patterns. For Fe and Mn, atmospheric depositions masked a classical nutrient type profile, while Cd was very depleted at the surface and concentrations steadily increased with depth. Cd was highly correlated to Phosphate (hereafter referred to as P). The Cd/P ratio was mainly controlled by P with elevated concentrations at depth resulting in strongly differing ratios in surface and subsurface layers of 16.6 pmol / µmol and 237 pmol / µmol, respectively. The complex photochemical processes during the dissolution of Mn dust are also subject of manuscript 4. This paper describes a mesocosm project in the Mediterranean with two consecutive additions of evapocondensed dust conducted. The data also show that the dissolution and loss rates of Mn were comparable during both seedings. The calculated fractional solubilities for the first and the second dust addition were 41 ± 9 % and 27 ± 19 %, respectively. The results presented in this thesis have significantly improved our understanding of Mn distribution and especially cycling in the euphotic zone. An insight into the mechanisms between Mn and ROS and into the dissolution processes from dust is given.Das Spurenelement Mangan (Mn) ist von zentraler Bedeutung im Meer, da es ein essenzieller Mikronährstoff für Phytoplankton ist. Es spielt eine wichtige Rolle im Photosystem II (PSII) bei der Sauerstoffbildung aus Wasser in der Photosynthese. Des Weiteren ist Mn wichtig für weitere enzymatische Redoxprozesse, insbesondere als aktives Metallzentrum in Superoxiddismutase (SOD), welche als intrazelluläre Schutzmechanismen vor oxidativem Stress durch photochemisch produziertes Superoxid (O2 ) fungieren. Im Meerwasser kommt Mn in drei Oxidationsstufen vor: in erster Linie als lösliches Mn(II), als unlösliches Mn(III) und als Mn(IV)-Oxide. Der biogeochemische Kreislauf von Mn im lichtdurchfluteten Ozean ist signifikant durch reaktive Sauerstoffspezies (ROS) beeinflusst. Hierbei können das stark reaktive und kurzlebige Superoxid (O2 ) und seine Tochterprodukt Wasserstoffperoxid (H2O2) gleichermaßen eine oxidierende als auch eine reduzierende Wirkung haben und spielen somit eine Schlüsselrolle für Mn Prozesse im Meerwasser. Im offenen Ozean beispielsweise ist atmosphärischer Staub die Haupteintragsquelle für Mn und das in oxidierter Form vorliegende Mn im Staub kann durch photochemisch gebildetes H2O2 reduziert und als Mn(II) im Wasser gelöst werden. Obwohl die groben Zusammenhänge dieser Prozesse bekannt sind, sind die Hauptreaktionen und Mechanismen des Zusammenspiels von Mn und ROS im Meerwasser kaum verstanden. Die Dissertation umfasst vier Manuskripte. Manuskripte 1 (Wuttig et al., subm., 2013a) und 2 (Wuttig et al., subm., 2013b) konzentrieren sich auf Kreisläufe und Reaktionsmechanismen von Mn und ROS. Manuskript 3 beschreibt die Unterschiede zwischen den Eintragsprozessen und der Verteilung von Cd, Fe und Mn im östlichen tropischen Atlantik nahe den Kapverdischen Inseln (Wuttig et al., in prep., 2013). Manuskript 4 (Wuttig et al., 2013) widmet sich der Untersuchung des Mn Kreislaufs in Folge der wiederholten Staubzugabe in das oligotrophe Oberflächenwasser von spurenmetall-sauberen Mesokosmen im Mittelmeer. Im Gegensatz zu früheren Beobachtungen im Südpolarmeer, konnte in dieser Studie klar gezeigt werden, dass im östlichen tropischen Atlantik Mn und organische Substanzen als vorwiegende Senken für O2 darstellen (Manuskript 1; Wuttig et al., subm., 2013a). Mn dominiert diesen Zerfall besonders im Oberflächenwasser, welches stark durch atmosphärischen Staubfluss beeinflusst ist, und nahe dem Meeresboden durch die Resuspension aus dem Sediment. Zudem konnte gezeigt werden, dass der Abbau von O2 durch Reaktion mit anorganischem Mn(II) in Seewasser einer Zerfallsrate erster Ordnung folgt (Manuskript 2, Wuttig et al., subm., 2013b). Diese scheint eine katalytische Reaktion des Mn(II)/MnO2+ Paars zu beinhalten, wobei MnO2+ der Superoxidkomplex ist. Des Weiteren ist es in der euphotischen und sauerstoffreichen Zone unwahrscheinlich, nennenswerte Mn(III) Konzentrationen aufzufinden, welche ohne starke Mn(III) bindende Liganden nur unter anoxischen Bedingungen erwartet werden. Somit kann Mn(III) im Gegensatz zum Mn(II)/MnO2+ Paar im sauerstoffreichen Oberflächenwasser nicht als SOD agieren. Atmosphärischer Staub ist die Haupteintragsquelle von Mn im Oberflächenwasser des östlichen tropischen Atlantiks (Manuskript 3; Wuttig et al., in prep., 2013). Jedoch wurden in dieser Region zusätzlich auch Einträge von Mn durch äquatorialen Auftrieb und Resuspension aus dem Sediment beobachtet. Zusätzlich wurde hier kein sekundäres Mn(II) Maximum gefunden, welches bei gleichen Untersuchungen im östlichen tropischen Pazifik in 200 m Tiefe der Fall war und vermutlich durch eine Kombination aus Einträgen durch atmosphärischen Staub und laterale Transportprozesse verursacht wurde. Während atmosphärische Quellen dominierend den Mn und Fe Kreislauf beeinflussen, sind Cd Konzentrationen im tropischen Atlantik nicht durch Staubeintrag kontrolliert (Manuskript 3; Wuttig et al., in prep., 2013). Generell zeigten diese Spurenelemente unterschiedliche Verteilungsmuster. Während die für biologisch relevante Elemente zu erwartenden typischen nährstoffähnlichen Tiefenprofiele durch den atmosphärischen Eintrag von Fe und Mn überlagert wurden, waren die Cd Konzentrationen im Oberflächenwasser sehr niedrig und nahmen mit der Tiefe zu. Das Cd/P Verhältnis wurde dabei in erster Linie durch die in der Tiefe erhöhten P Konzentrationen bestimmt und wies dort ein Cd/P Verhältnis von 237 pmol / µmol gegenüber 16.6 pmol / µmol im Oberflächenwasser aus. Auch im Manuskript 4 (Wuttig et al., 2013), welches sich mit der Löslichkeit und dem Kreislauf von Mn nach zwei Zugaben prozessierten Staubs während eines Mesokosmen Projektes im Mittelmeer beschäftigt, spielen die komplexen photochemischen Experimente eine zentrale Rolle. Hinzukommend zeigen die Daten, dass die Mn Löslichkeits- und Verlustraten nach den beiden Staubzugaben vergleichbar sind. Die anteilige Löslichkeit von Mn aus dem Staubmaterial betrug 41 ± 9 % für die erste Staubzugabe und 27 ± 19 % für die zweite Staubzugabe

Reactivity of inorganic Mn and Mn Desferrioxamine B with O2, O2-and H2O2in seawater

Manganese (Mn) is a required element for oceanic phytoplankton as it plays a critical role in photosynthesis, through its unique redox chemistry, as the active site in photosystem II and in enzymes that act as defences against reactive oxygen species (ROS), most notably for protection against superoxide (O2-), through the action of superoxide dismutase (SOD), and against hydrogen peroxide (H2O2) via peroxidases and catalases. The distribution and redox speciation of Mn in the ocean is also apparently controlled by reactions with ROS. Here we examine the connections between ROS and dissolved Mn species in the upper ocean using field and laboratory experimental data. Our results suggest it is unlikely that significant concentrations of Mn(III) are produced in the euphotic zone, as in the absence of evidence for the existence of strong Mn(III) ligands, Mn(II) reacts with O2- to form the short lived transient manganous superoxide, MnO2+, which may react rapidly with other redox species in a similar manner to O2-. Experiments with the strong Mn(III) chelator, desferrioxamine B (DFB), in seawater indicated that the Mn(III) species is unlikely to form, as the pre-cursor Mn(II) complex under natural ambient conditions due to the high side reaction of DFB with Ca

Impacts of dust deposition on dissolved trace metal concentrations (Mn, Al and Fe) during a mesocosm experiment

The deposition of atmospheric dust is the primary process supplying trace elements abundant in crustal rocks (e.g. Al, Mn and Fe) to the surface ocean. Upon deposition, the residence time in surface waters for each of these elements differs according to their chemical speciation and biological utilization. Presently, however, the chemical and physical processes occurring after atmospheric deposition are poorly constrained, principally because of the difficulty in following natural dust events in situ. In the present work we examined the temporal changes in the biogeochemistry of crustal metals (in particular Al, Mn and Fe) after an artificial dust deposition event. The experiment was contained inside trace metal clean mesocosms (0–12.5 m depths) deployed in the surface waters of the northwestern Mediterranean, close to the coast of Corsica within the frame of the DUNE project (a DUst experiment in a low Nutrient, low chlorophyll Ecosystem). Two consecutive artificial dust deposition events, each mimicking a wet deposition of 10 g m−2 of dust, were performed during the course of this DUNE-2 experiment. The changes in dissolved manganese (Mn), iron (Fe) and aluminum (Al) concentrations were followed immediately after the seeding with dust and over the following week. The Mn, Fe and Al inventories and loss or dissolution rates were determined. The evolution of the inventories after the two consecutive additions of dust showed distinct behaviors for dissolved Mn, Al and Fe. Even though the mixing conditions differed from one seeding to the other, Mn and Al showed clear increases directly after both seedings due to dissolution processes. Three days after the dust additions, Al concentrations decreased as a consequence of scavenging on sinking particles. Al appeared to be highly affected by the concentrations of biogenic particles, with an order of magnitude difference in its loss rates related to the increase of biomass after the addition of dust. In the case of dissolved Fe, it appears that the first dust addition resulted in a decrease as it was scavenged by sinking dust particles, whereas the second seeding induced dissolution of Fe from the dust particles due to the excess Fe binding ligand concentrations present at that time. This difference, which might be related to a change in Fe binding ligand concentration in the mesocosms, highlights the complex processes that control the solubility of Fe. Based on the inventories at the mesocosm scale, the estimations of the fractional solubility of metals from dust particles in seawater were 1.44 ± 0.19% and 0.91 ± 0.83% for Al and 41 ± 9% and 27 ± 19% for Mn for the first and the second dust addition. These values are in good agreement with laboratory-based estimates. For Fe no fractional solubility was obtained after the first seeding, but 0.12 ± 0.03% was estimated after the second seeding. Overall, the trace metal dataset presented here makes a significant contribution to enhancing our knowledge on the processes influencing trace metal release from Saharan dust and the subsequent processes of bio-uptake and scavenging in a low nutrient, low chlorophyll are

The Stability of Fe-Isotope Signatures During Low Salinity Mixing in Subarctic Estuaries

We have studied iron (Fe)-isotope signals in particles (> 0.22 µm) and the dissolved phase (< 0.22 µm) in two subarctic, boreal rivers, their estuaries and the adjacent sea in northern Sweden. Both rivers, the Råne and the Kalix, are enriched in Fe and organic carbon (up to 29 µmol/L and up to 730 µmol/L, respectively). Observed changes in the particulate and dissolved phase during spring flood in May suggest different sources of Fe to the rivers during different seasons. While particles show a positive Fe-isotope signal during winter, during spring flood, the values are negative. Increased discharge due to snowmelt in the boreal region is most times accompanied by flushing of the organic-rich sub-surface layers. These upper podzol soil layers have been shown to be a source for Fe-organic carbon aggregates with a negative Fe-isotope signal. During winter, the rivers are mostly fed by deep groundwater, where Fe occurs as Fe(oxy)hydroxides, with a positive Fe-isotope signal. Flocculation during initial estuarine mixing does not change the Fe-isotope compositions of the two phases. Data indicate that the two groups of Fe aggregates flocculate diversely in the estuaries due to differences in their surface structure. Within the open sea, the particulate phase showed heavier δ56Fe values than in the estuaries. Our data indicate the flocculation of the negative Fe-isotope signal in a low salinity environment, due to changes in the ionic strength and further the increase of pH

Circulation and Oxygen Distribution in the Tropical Atlantic Cruise No. 80, Leg 1; October 26 to November 23, 2009 Mindelo (Cape Verde) to Mindelo (Cape Verde)

METEOR cruise 80/1 was a contribution to the SFB 754 “Climate-Biogeochemistry Interactions in the Tropical Ocean”. Shipboard, glider and moored observations are used to study the temporal and spatial variability of physical and biogeochemical parameters within the oxygen minimum zone (OMZ) of the tropical North Atlantic. As part of the BMBF “Nordatlantik” project, it further focuses on the equatorial current system including the Equatorial Undercurrent (EUC) and intermediate currents below. During the cruise, hydrographic station observations were performed using a CTD/O2 rosette, including water sampling for salinity, oxygen, nutrients and other biogeochemical tracers. Underway current measurements were successfully carried out with the 75 kHz ADCP borrowed from R/V POSEIDON during the first part of the cruise, and R/V METEOR’s 38 kHz ADCP during the second part. During M80/1, an intensive mooring program was carried out with 8 mooring recoveries and 8 mooring deployments. Right at the beginning of the cruise, a multidisciplinary mooring near the Cape Verde Islands was recovered and redeployed. Within the framework of SFB 754, two moorings with CTD/O2 profilers were recovered and redeployed with other instrumentation in the center and at the southern rim of the OMZ of the tropical North Atlantic. The equatorial mooring array as part of BMBF “North Atlantic” project consists of 5 current meter moorings along 23°W between 2°S and 2°N. It is aimed at quantifying the variability of the thermocline water supply toward the equatorial cold tongue which develops east of 10°W during boreal summer. Several glider missions were performed during the cruise. One glider was recovered that was deployed two months earlier. Another glider was deployed for two short term missions, near the equator for about 8 days and near 8°N for one day. This glider was equipped with a new microstructure probe in addition to standard sensors, i.e. CTD/O2, chlorophyll and turbidity

Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES-Era Data

86 pages, 33 figures, 2 tables, 1 appendix.-- Data Availability Statement: The majority of the dissolved data were sourced from the GEOTRACES Intermediate Data Products in 2014 (Mawji et al., 2015) and 2017 (Schlitzer et al., 2018), and citations to the primary data sources are given in the caption for each figure. Data sources for Figure 1 are given below. Figure 1: Iron: Conway & John, 2014a (Atlantic); Conway & John, 2015a (Pacific); Abadie et al., 2017 (Southern). Zinc: Conway & John, 2014b (Atlantic); Conway & John, 2015a (Pacific); R. M. Wang et al., 2019 (Southern). Copper: Little et al., 2018 (Atlantic); Takano et al., 2017 (Pacific); Boye et al., 2012 (Southern). Cadmium: Conway and John, 2015b (Atlantic); Conway & John, 2015a (Pacific); Abouchami et al., 2014 (Southern). Molybdenum: Nakagawa et al., 2012 (all basins). Barium: Bates et al., 2017 (Atlantic); Geyman et al., 2019 (Pacific); Hsieh & Henderson, 2017 (Southern). Nickel: Archer et al., 2020 (Atlantic); Takano et al., 2017 (Pacific); R. M. Wang et al., 2019 (Southern). Chromium: Goring-Harford et al., 2018 (Atlantic); Moos & Boyle, 2019 (Pacific); Rickli et al., 2019 (Southern). Silver: Fischer et al., 2018 (Pacific); Boye et al., 2012 (Southern)Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate historyThis contribution grew (and grew) out of a joint workshop between GEOTRACES and Past Global Changes (PAGES) held in Aix-en-Provence in December 2018. The workshop was funded by the U.S. National Science Foundation (NSF) through the GEOTRACES program, the international PAGES project, which received support from the Swiss Academy of Sciences and NSF, and the French program Les Envelopes Fluides et l'Environnement. [...] T. J. Horner acknowledges support from NSF; S. H. Little from the UK Natural Environment Research Council (NE/P018181/1); T. M. Conway from the University of South Florida; and, J. R. Farmer from the Max Planck Society, the Tuttle Fund of the Department of Geosciences of Princeton University, the Grand Challenges Program of the Princeton Environmental Institute, and the Andlinger Center for Energy and the Environment of Princeton University. [...] With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S