New insights into productivity and redox‐controlled trace element (Ag, Cd, Re, and Mo) accumulation in a 55 kyr long sediment record from Guaymas Basin, Gulf of California

Abstract

A high-resolution, 55 kyr long record of chalcophile and redox-sensitive trace element accumulation (Ag, Cd, Re, and Mo) from MD02-2515, western Guaymas Basin, is investigated in conjunction with patterns in stratigraphy and productivity. High opal concentrations (~59 wt. %), representing increased diatom production, coincide with laminated sediments and dilute the concentrations of organic carbon (C org ) and metals. A similarity between opal and normalized C org , Ag, and Cd concentrations suggests delivery to the sediments by diatom export production, while patterns in normalized Re and Mo accumulation suggest a different emplacement mechanism. Although Mo enrichment in organic-rich, laminated sediments typically represents anoxic conditions at other locations, Mo (and Re) in Guaymas Basin is enriched in nonlaminated and bioturbated sediments that are representative of oxygenated conditions. Adsorption onto Fe-and/or Mn-oxyhydroxide surfaces during oxygenation inadequately explains both the Re and Mo enrichments. Thus, recently published mechanisms invoking direct Re and Mo removal from the water column and bioturbation-assisted irrigation of Re into the sediments are used to explain the counterintuitive observations in Guaymas Basin. The MD02-2515 stratigraphic and proxy records are also different from other records in the northeast Pacific in that there is little correspondence with Greenland Dansgaard-Oeschger interstadials. There is some correlation with Heinrich events, suggesting that ventilation of intermediate waters and/or reduced productivity may be important in controlling stratigraphy and trace element accumulation. The results question whether MD02-2515 records can be compared to northeast Pacific open-margin records, especially before 17 kyr B.P.

The simulated climate of the Last Glacial Maximum and insights into the global marine carbon cycle

“…The net decline in export production observed in this study was dominated by the decline in tropical and subtropical waters. Many palaeoproductivity studies located outside of the subantarctic zone have found weakened productivity at the LGM (Chang et al, 2014(Chang et al, , 2015Costa et al, 2016;Crusius et al, 2004;Kohfeld et al, 2005;Kohfeld and Chase, 2011;Jaccard et al, 2005;McKay et al, 2015;Ortiz et al, 2004;Riethdorf et al, 2013;Salvatteci et al, 2016;Singh et al, 2011;Thomas et al, 1995). Additionally, an enhanced utilisation of available nutrients in the subantarctic zone would reduce the nutrient content of intermediate waters formed in the Southern Ocean and would thus reduce the delivery of nutrients to lower latitudes (Sarmiento et al, 2004).…”

Comparisons between marine productivity and terrestrial input records in the Gulf of California over the last 28 ka

“…(2005) (Barron et al ., 2004; Keigwin & Jones, 1990; Pride et al ., 1999); data from Core MD02‐2515 as in Chang et al . (2015) (Cheshire & Thurow, 2013; Pichevin et al ., 2014), Core JPC20 data ( this study ) show a 3‐point running average. Black arrows show increases/decreases in percentages of biogenic components during stadial events.…”

“…8G). In terms of biological productivity, a regional decrease in biogenic silica occurred during H2, H1 and YD events, but increase during B/A, as previously recognised (Barron et al ., 2005, 2014; Chang et al ., 2015; McClymont et al ., 2012; Pichevin et al ., 2014). As a general hypothesis, a change toward warmer sea surface temperatures (SST) can mirror an upwelling reduction, due to the latitudinal displacement of the ITCZ and a weaker subtropical jet that impedes winter to early spring upwelling from developing (Barron et al ., 2014; McClymont et al ., 2012; Oster et al ., 2015; Pichevin et al ., 2014).…”

“…However, interlaboratory comparisons suggest that no significant differences exist when this widely used technique is applied to quantify biogenic silica in sediment (Conley, 1998). Furthermore, the Mortlock and Froelich (1989) wet digestion technique has been commonly and successfully used to measure biogenic silica in sediment from the GC (Chang et al ., 2015; Cheshire & Thurow, 2013; Douglas et al ., 2007; Keigwin & Jones, 1990; Pride et al ., 1999; Thunell, 1998).…”

“…Numbers show rivers along the coast. Red star indicates the location of Core AII‐125‐8‐JPC20 and green symbols show the location of other cores previously studied (Barron et al ., 2004; Chang et al ., 2015; Cheshire & Thurow, 2013; Keigwin & Jones, 1990; Pichevin et al ., 2014; Pride et al ., 1999; Staines‐Urías et al ., 2015). (C) Location of Core AII‐125‐8‐JPC20 in the Carmen Basin (latitude 26.039°N, longitude 110.93°W), bathymetric features, depth (m) and distance scale (km).…”