Spatio-temporal distribution and transport of particulate matter in the eastern tropical North Atlantic observed by Argo floats.

Ohde, Thomas, Fiedler, Björn and Körtzinger, Arne (2015) Spatio-temporal distribution and transport of particulate matter in the eastern tropical North Atlantic observed by Argo floats. Deep-Sea Research Part I-Oceanographic Research Papers, 102 . pp. 26-42. DOI 10.1016/j.dsr.2015.04.007.

[img] Text
ohde et al 2015.pdf - Published Version
Restricted to Registered users only

Download (5Mb) | Contact

Supplementary data:

Abstract

Highlights:
• The distribution of particulate matter was studied using Argo float measurements.
• Its spatio-temporal properties were analyzed in the eastern tropical North Atlantic.
• Surface, subsurface, intermediate and bottom nepheloid layers were considered.
• High correlations between particulate matter and phytoplankton were verified.
• The depth of subsurface particle maxima correlated to the distance to shore.

Abstract:
The spatial and temporal distribution of particulate matter in the water column of the eastern tropical North Atlantic between 16.9–22.9°N and 16.6–29.3°W was investigated using optical measurements from transmissometers mounted on Argo floats. The corresponding profiles of beam attenuation coefficients measured from February 2008 to May 2009 were used to study particulate matter in different layers such as the surface nepheloid layer (SNL), subsurface nepheloid layer (SSNL), intermediate nepheloid layer (INL) and bottom nepheloid layer (BNL) as well as to investigate sinking particles (SP).

The SNL were down to about 60 m water depth at thicknesses between 20 and 60 m. Our analyses verified high correlation between particulate matter and phytoplankton in the SNL. High offshore SNL extension of up to 750 km was found in the area of Cape Blanc filaments in January 2009. Their typical widths ranged from 11 to 72 km. Furthermore, float-borne observations even resolved atmospheric dust deposition into the surface water layer during a strong Saharan dust event in October 2008. The observed dust concentration in the mixed water layer was found to vary between 0.0021 and 0.0168 g m−3 depending on applied assumptions.

An abrupt change from a SNL to a SSNL regime over distances of only 80 to 90 km was observed. The particulate matter in the SSNL showed lateral extensions from 420 to 1020 km offshore. A statistically significant correlation between the depth of subsurface particle maxima and the distance to shore was found.

An averaged diameter of 30 km was determined for the sharply isolated patches of INL which was consistent with model simulations of other studies. The lateral transport of particulate matter in these INL features in the area of the giant Cape Blanc filaments was found to be more pronounced than reported in earlier studies. The distribution of particulate matter within the INL filaments reached up to 610 km off the shelf edge. The frequency of INL decreased with increasing distance to shore. The sinking velocity of particulate matter of one long-term observed INL was approximately 1.3 m day−1. Highly concentrated BNLs with beam attenuation coefficients of up to 4.530 m−1 were observed in the continental slope region. INLs appeared more frequently than SP events which lead to the conclusion that the lateral transport of particulate matter in INL features in the study area was more important than their passive vertical sinking.

Document Type: Article
Funder compliance: e.g. info:eu-repo/grantAgreement/EC/FP7/511176
Keywords: Argo Profiling floats; Transmissometer; Particulate matter; Nepheloid layer; INL; BNL; Saharan dust; Lateral transport; Eastern tropical North Atlantic
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.dsr.2015.04.007
ISSN: 0967-0637
Projects: SOPRAN, CARBOOCEAN, Future Ocean
Date Deposited: 06 May 2015 09:27
Last Modified: 19 Dec 2017 12:46
URI: http://oceanrep.geomar.de/id/eprint/28743

Actions (login required)

View Item View Item

Document Downloads

More statistics for this item...