Evolution of fluid flow and carbonate recrystallization rates in deep-sea sediments of the Equatorial Pacific

Andreas Wittke,Nikolaus Gussone,Barbara M A Teichert,Dominik Derigs

doi:10.1007/s00367-021-00720-9

Abstract

Fluid flow and carbonate recrystallization rates of deep-sea sediments from eight locations in the Equatorial Eastern Pacific were determined by using δ44/40Ca values of pore water and corresponding sediments. The studied drill sites of IODP Exp. 320/321 are located along a transect of decreasing crustal age and reveal different characteristic pore water depth profiles. The younger sites show an overall isotopic equilibration with the sediment in the upper part of the sedimentary column. In the lower part, the δ44/40Ca of the pore water increases back to seawater-like values at the sediment/basalt interface, forming a bulge-shaped pore water profile. The magnitude of the δ44/40Ca pore water bulge decreases with increasing age of the oceanic crust and sediment cover, resulting in seawater-like δ44/40Ca values throughout the sedimentary column in the oldest Sites U1331 and U1332. These findings indicate a seawater-like fluid input from the underlying crust into the sediment. Thus, after sedimentation, carbonate recrystallization processes start to enrich the pore water in 40Ca, and after a time of carbonate recrystallization and cooling of oceanic crust, a flow of seawater-like fluid starts to move upwards through the sedimentary column, enriching the pore water with 44Ca. We established a carbonate recrystallization and fluid flow model to quantify these processes. Our determined carbonate recrystallization rates between 0.000013e(−t/15.5) and 0.00038e(−t/100.5) and fluid flow rates in the range of 0.42–19 m*Myr−1 indicate that the fluid flow within the investigated sites of IODP Exp. 320/321 depends on the sedimentary composition and location of the specific site, especially the proximity to a recharge or discharge site of a hydrothermal convection cell.

Highlights

IntroductionWilhelms-Universität Münster, Münster, Germany 5 Agricola Hochschule Bochum, Bochum, Germany depleted clay sediments (Berger 1989; Bowles et al 2014)
Over 70% of the Earth’s surface is covered by water and the largest part of the ocean basin is covered by deep-sea sediments, which consist of up to 70% of organic carbonGermany 4 Institut für Geologie und Paläontologie, WestfälischeWilhelms-Universität Münster, Münster, Germany 5 Agricola Hochschule Bochum, Bochum, Germany depleted clay sediments (Berger 1989; Bowles et al 2014)
To better constrain C aCO3 recrystallization rates and fluid movements within sediment that may be affected by hydrothermal fluid flow, we investigated the Ca isotope composition of pore water and bulk carbonate sediment of all eight deep-sea sediment cores of IODP Exp. 320/321

Summary

Introduction

Wilhelms-Universität Münster, Münster, Germany 5 Agricola Hochschule Bochum, Bochum, Germany depleted clay sediments (Berger 1989; Bowles et al 2014). These sediments are a significant reservoir of the marine realm and diagenetic reactions taking place within, playing an important role in geochemical cycling in the Earth’s system. Some of these reactions, for example, microbial redox reactions or abiotic reactions in the fluid phase such as dissolution or precipitation, imprint characteristic patterns of reactants in sedimentary pore water (PW). The hypothesis of hydrothermally driven fluid flow through the oceanic crust has been developed (e.g., Bekins et al 2007; Fisher et al 2003; Fisher 2004; Fisher 2005; Villinger et al, 2016; Wheat et al 2002) suggesting that (inactive) seamounts or bathymetric pits take up and heat up the seawater

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