Particle dynamics in the rising plume at Piccard Hydrothermal Field, Mid‐Cayman Rise

Abstract

Processes active in rising hydrothermal plumes, such as precipitation, particle aggregation, and biological growth, affect particle size distributions and can exert important influences on the biogeochemical impact of submarine venting of iron to the oceans and their sediments. However, observations to date of particle size distribution within these systems are both limited and conflicting. In a novel buoyant hydrothermal plume study at the recently discovered high-temperature (3988C) Piccard Hydrothermal Field, MidCayman Rise, we report optical measurements of particle size distributions (PSDs). We describe the plume PSD in terms of a simple, power-law model commonly used in studies of upper and coastal ocean particle dynamics. Observed PSD slopes, derived from spectral beam attenuation and laser diffraction measurements, are among the highest found to date anywhere in the ocean and ranged from 2.9 to 8.5. Beam attenuation at 650 nm ranged from near zero to a rarely observed maximum of 192 m 21 at 3.5 m above the vent. We did not find large (>100 lm) particles that would settle rapidly to the sediments. Instead, beam attenuation was well-correlated to total iron, suggesting the first-order importance of particle dilution, rather than precipitation or dissolution, in the rising plume at Piccard. Our observations at Piccard caution against the assumption of rapid deposition of hydrothermal, particulate metal fluxes, and illustrate the need for more particle size and composition measurements across a broader range of sites, globally.

Unusually low234Th in a hydrothermal effluent plume over the Southwest Indian Ridge

“…Earlier studies indicated that Fe and Mn oxyhydroxides are important for the scavenging of dissolved seawater constituents in the hydrothermal plumes [ Berner , ; Trefry and Metz , ]. These particles also disperse with the plume [ Dymond , ; Feely et al ., , ; Wang et al ., ; Estapa et al ., ], and are probably transported hundreds of kilometers, as observed in the deep Pacific Ocean [ Siegel et al ., ]. Toner et al .…”

“…To date, three active zones, extending laterally 1000 m, have been found [Tao et al, 2012]. Since limited hydrothermal vents have been confirmed on ultraslow-spreading ridges [German et al, 1998;Tao et al, 2012], their influence on either heat balance or chemical budgets in the global oceans has received only limited examination [Bach et al, 2002;Estapa et al, 2015]. A few studies indicate that a hydrothermal effluent plume on the ultraslowspreading ridge (i.e., Gakkel Ridge in the Arctic Ocean) also adds large amounts of chemicals to oceans in a manner similar to that of fast-spreading ridges [German et al, 1998;Edmonds et al, 2003;Statham et al, 2005].…”

Utilizing 210Po deficit to constrain particle dynamics in mesopelagic water, western South China Sea

“…The residence times of particulate 210 Po at the slope stations (i.e., 105A and 91) ranged from 0.11 to 0.16 year within the mesopelagic layer (averaging 0.13 ± 0.04 year), comparable to the residence times of TPM in a hydrothermal plume over the Southwest Indian Ridge [ Yang et al ., ]. Such a time scale allows particulate matter to move over a very long range as proved in general deep water [ Siegel et al ., ] and in the mesopelagic or bathypelagic hydrothermal plumes [ Wang et al ., ; Estapa et al ., ]. Thus, the residence times of particulate 210 Po provide supports for the transport of resuspended shelf sediment into the SCS basin.…”

Quartz Solubility in the Two‐Phase Region of the NaCl‐H2O System: An Experimental Study With Application to the Piccard Hydrothermal Field, Mid‐Cayman Rise

“…However, as emphasized by Rudnicki and German (2002), plume heights can vary with time. Estapa et al (2015) place the maximum plume height at approximately 4,100 m depth, 150 m below the value of German, Bowen, et al (2010), although it is possible that the plume rises higher than this given the apparent uncertainties. To compensate for changes in the maximum height, we use 3,950 ± 150 m as the top of the Piccard plume.…”