TY - JOUR
T1 - Molybdenum and uranium geochemistry in continental margin sediments
T2 - Paleoproxy potential
AU - McManus, James
AU - Berelson, William M.
AU - Severmann, Silke
AU - Poulson, Rebecca L.
AU - Hammond, Douglas E.
AU - Klinkhammer, Gary P.
AU - Holm, Chris
N1 - Funding Information: Many individuals have provided invaluable assistance during the cruises when these data were collected, those individuals are too numerous to mention here, but their contributions are no less important to the success of our work. The captains and crews of the R.V. Pt. Sur, R.V. New Horizon, and R.V. Roger Revelle are all extended sincere gratitude for their tireless efforts collecting the sediments, and we note our use of the Pt. Sur on multiple occasions. A number of senior colleagues also participated in collecting the samples used during this study and were gracious with their time and effort at sea and we acknowledge them: Kenneth Johnson, Kenneth Coale, Alan Mix, Nick Pisias, and David Burdige. Bobbi Conard, Andy Ross, and Andy Ungerer provided invaluable analytical support for many of the measurements made in the laboratory. Finally, it is impossible to acknowledge all in the scientific community who have had an impact on the development of the ideas presented here, however incomplete those ideas may yet be. We therefore acknowledge the thoughtful discussions and criticisms of the many who have been willing to ask the provocative question or offer guidance. Their unselfish cooperation is appreciated. Associate Editor Tim Shaw, Jennifer Morford, Lex van Geen, Hans Brumsack, and six anonymous reviewers provided constructive criticism on early versions of this manuscript. This research was supported by NSF Grants OCE-0219651 and OCE-9911550 to the lead P.I. and OCE-9617929 to J.M. and G.P.K.; NSF Grants OCE-0002250 and OCE-0129555 to W.M.B.
PY - 2006/9/15
Y1 - 2006/9/15
N2 - We measured solid-phase Mo and U concentrations in marine sediments from the California, Mexico, Peru, and Chile margins to ascertain the behavior of Mo and U during early diagenesis in continental margin settings. At sites along the California, Mexico, and Peru margins where there are estimates of mass accumulation rates, authigenic U accumulation rates range from ∼0-50 nmol m-2 day-1. At the California and Mexico margin sites Mo accumulation rates range from 0 to 134 nmol m-2 day-1 whereas at the Peru margin site rates may be as high as 550 nmol m-2 day-1. We observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon (Corg). In the case of Mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial. For most of the data presented in this manuscript, continental margin sediments have a Mo:Corg accumulation rate ratio of ∼20 μmol mol-1. This value is significantly lower, however, than those reported for anoxic basins ∼100 μmol mol-1, but is consistent with reported Mo:Corg rain ratios from Mexico margin sediment traps. In contrast to Mo, there appears to be a single U:Corg burial ratio of ∼5 μmol mol-1, which includes a range of environments from anoxic basins and open ocean sites. We interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings. However, we note that any relationship between metal accumulation and organic carbon could be indirect. In the particular case of Mo, based on what is known about Mo geochemistry from the literature, it is possible that Mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study, and that the observed association between Mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial. Using the observed relationships between Mo and Corg burial as well as constraints from the Mo isotope budget we estimate that continental margin sediments are an important sink for Mo. The magnitude of this sink (∼0.4 × 108 mol y-1, or larger) may be as much as one quarter of the oceanic removal term, and is likely to be larger than the modern anoxic basin sink.
AB - We measured solid-phase Mo and U concentrations in marine sediments from the California, Mexico, Peru, and Chile margins to ascertain the behavior of Mo and U during early diagenesis in continental margin settings. At sites along the California, Mexico, and Peru margins where there are estimates of mass accumulation rates, authigenic U accumulation rates range from ∼0-50 nmol m-2 day-1. At the California and Mexico margin sites Mo accumulation rates range from 0 to 134 nmol m-2 day-1 whereas at the Peru margin site rates may be as high as 550 nmol m-2 day-1. We observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon (Corg). In the case of Mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial. For most of the data presented in this manuscript, continental margin sediments have a Mo:Corg accumulation rate ratio of ∼20 μmol mol-1. This value is significantly lower, however, than those reported for anoxic basins ∼100 μmol mol-1, but is consistent with reported Mo:Corg rain ratios from Mexico margin sediment traps. In contrast to Mo, there appears to be a single U:Corg burial ratio of ∼5 μmol mol-1, which includes a range of environments from anoxic basins and open ocean sites. We interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings. However, we note that any relationship between metal accumulation and organic carbon could be indirect. In the particular case of Mo, based on what is known about Mo geochemistry from the literature, it is possible that Mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study, and that the observed association between Mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial. Using the observed relationships between Mo and Corg burial as well as constraints from the Mo isotope budget we estimate that continental margin sediments are an important sink for Mo. The magnitude of this sink (∼0.4 × 108 mol y-1, or larger) may be as much as one quarter of the oceanic removal term, and is likely to be larger than the modern anoxic basin sink.
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U2 - https://doi.org/10.1016/j.gca.2006.06.1564
DO - https://doi.org/10.1016/j.gca.2006.06.1564
M3 - Article
VL - 70
SP - 4643
EP - 4662
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
SN - 0016-7037
IS - 18
ER -