Hawaii Ocean Time-series (HOT)
in the School of Ocean and Earth Science and Technology at the University of Hawai'i

Bottom-Moored Sediment Traps

Bottom-moored traps

Analytical Method

A bottom-moored sediment trap experiment has been in place since June 1992 at a site near Station ALOHA. Schedule of deployments and retrievals is shown in Table 1 below. The ALOHA-XX mooring was deployed in May 2017. The present experiment consists of 2 Parflux MK7-21 sequencing sediment collectors locate at 2800 m & 4000 m. A separate sampling cup will be rotated into the collector position on an approximately 10-20 day cycle, depending on the deployment period. Samples from each cup will initially be divided into four 60-ml volumes (also refered to as splits). Each split will further be divided into the volumes required for the various analysis.


Designation Location Depth Schedule
ALOHA-I 22 57.3'N, 158 06.2'W 4,800 Jun 1992 - Sep 1993
ALOHA-II 23 06.7'N, 157 55.8'W 4,800 Sep 1993 - Oct 1994
ALOHA-III 22 50.2'N, 157 55.9'W 4,800 May 1995 - Oct 1995
ALOHA-IV 22 51.7'N, 157 54.3'W 4,800 Nov 1995 - Oct 1996
ALOHA-V 22 51.0'N, 157 53.7'W 4,800 Oct 1996 - Dec 1997
ALOHA-VI 22 51.5'N, 157 55.8'W 4,800 Dec 1997 - Nov 1998
ALOHA-VII 22 51.8'N, 157 55.4'W 4,800 Nov 1998 - Oct 1999
ALOHA-VIII 22 49.3'N, 157 52.5'W 4,800 Nov 1999 - Nov 2000
ALOHA-IX 22 48.7'N, 157 54.1'W 4,800 Dec 2000 - Mar 2002
ALOHA-X 22 48.3'N, 157 55.3'W 4,800 Jun 2002 - Jun 2003
ALOHA-XI 22 50.5'N, 157 52.4'W 4,800 Nov 2003 - Mar 2005
ALOHA-XII 22 49.7'N, 158 05.1'W 4,800 Jul 2005 - Sep 2005
ALOHA-XIII 22 51.5'N, 157 55.1'W 4,800 Jun 2007 - Aug 2008
ALOHA-XIV 22 51.7'N, 157 55.1'W 4,800 Jun 2009 - Sep 2009
ALOHA-XV 22 51.8'N, 157 53.3'W 4,800 Jun 2009 - Sep 2009
ALOHA-XVI 22 50.9'N, 157 54.0'W 4,800 May 2012 - Oct 2012
ALOHA-XVII 22 50.3'N, 157 54.8'W 4,800 Mar 2014 - Dec 2014
ALOHA-XVIII 22 50.9'N, 157 54.4'W 4,800 Apr 2015 - Dec 2015
ALOHA-XIX 22 50.2'N, 157 55.4'W 4,800 May 2016 - Dec 2016
ALOHA-XX 22 52.0'N, 157 53.2'W 4,800 May 2017 - Dec 2017

Table 1: Schedule of Deployments and Recoveries of Moored Sediment Trap


Results

Particulate carbon flux measurements from the ALOHA-I and II sediment traps is shown in Figure 65. Particulate carbon, as well as particulate nitrogen, phosphorus and mass, showed a major export pulse during the summer periods when the upper water column was well stratified. A second export pulse was also observed in late winter-early spring but this feature appears to be different than the summer peak. The major particulate matter export was recorded in the same collector cups regardless of depth suggesting a sinking rate of about 200 m d-1. Analysis of chlorophyll a by fluorometry and HPLC pigment analyses reveal that the peak export event coincides with the removal of pigmented cells. The summer export material contains the full spectrum of major and accessory pigments. Microscopic analysis showed the dominance of diatoms during the summer export. A discussion of some of the findings has been presented in Karl et al. (1996a and 1997).