DOI: 10.25921/sepx-n678
title: NOAA/WDS Paleoclimatology - Guaymas Basin 17KYr High Resolution Geochemical Data

description: Sediments deposited on the western slope of the Guaymas Basin in the central Gulf of California are composed predominantly of detrital clastic material and biogenic silica (biopal), with minor organic material (average of 2.8% organic carbon) and calcium carbonate. The CaCO3 is derived from calcareous plankton and is highly variable ranging from 0% to 16%. In general, the CaCO3 content of the sediments varies inversely with the biopal content, reflecting the relative abundance of calcareous and siliceous plankton in the photic zone. Siliceous plankton dominate when winds are predominantly out of the northwest producing strong upwelling. Calcareous plankton indicates weak southeasterly winds that bring warm, tropical Pacific surface water into the Gulf. Based mainly on relative abundances of biopal and CaCO3, the sediments deposited over the last 17,000 years in the western Guaymas Basin can be divided into five intervals. In general, the sediments in the intervals with high biopal and low CaCO3 are laminated, but this is not always true. Unlike most other continental margins of the world with well-developed oxygen minimum zones where highest concentrations of organic carbon and redox-sensitive trace metals occur in laminated sediments, the laminated sediments on the anoxic slope of the western Guaymas Basin do not always have the highest concentrations of organic carbon and trace metals such as Mo and Cd.
description: Geochemical data from the Gulf of California, Guaymas Basin cores GGC55 and JPC56.

Giant gravity core (GGC) 55 and jumbo piston core (JPC) 56 are two of a series of paired, overlapping gravity and piston cores that were collected 
in July 1990 on R/V Atlantis II cruise 125/8. These two cores were collected on the western slope of the Guaymas Basin, GGC55 at 27deg28.22'N, 
112deg6.33'W in a water depth of 820m, and JPC56 at 27deg28.16'N, 112deg6.26'W in a water depth of 818m . Both cores were sampled at 10-cm intervals 
for geochemical  analyses.  The samples were analyzed for 40 major, minor, and trace elements by inductively coupled, argon plasma, atomic emission 
spectrometry (ICP-AES; Briggs, 2002).  Rock standards (USGS) were included with the sediment samples, and 10% of the samples were duplicated. 
The precision, determined by analyzing rock standards and duplicate sediment samples, is better than 10%, and usually is better than 5%, at a 
concentration of 10 times the limit of detection. Results for 8 major elements (in weight percent) and 19 minor and trace elements 
(in parts per million) are given here. 

Dried samples were analyzed for weight percentages of total carbon (TC) and inorganic carbon (IC) by coulometric titration of carbon dioxide following 
extraction from the sediment by combustion at 950C and acid volatilization, respectively (Engleman et al., 1985). Percent total organic carbon (% TOC) 
was calculated as the difference (TC-IC), and percent CaCO3 was calculated as CaCO3 1/4 IC=0:12; where 0.12 is the fraction of carbon in CaCO3. 
The accuracy and precision of this method, determined from hundreds of replicate standards, usually are better than 0.10% for both TC and IC.

Methods References 

Briggs, P.H., 2002. The determination of forty elements in geological and botanical samples by inductively coupled plasma-atomic emission spectrometry, 
In: Taggart, J.E., (Ed.), Analytical methods for chemical analyses of geologic and other materials, U.S. Geological Survey Open-File Report 02-223, pp. G1-20.

Engleman, E.E., Jackson, L.L., Norton, D.R., Fischer, A.G., 1985. Determination of carbonate carbon in geological materials by coulometric titration. 
Chemical Geology 53, 125-128.

Keigwin, L.D., 2002, Late Pleistocene-Holocene paleoceanography and ventilation of the Gulf of California:  Jour. Oceanog., v. 58, p. 421-432.