Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Data depth discrete in situ McLane pump casts illustrating filter sizes used and volumes filtered.

McLane WTS-LV08 in situ pumps were deployed on the CTD wire. Depth of deployment was determined by monitoring the depth of the CTD package and the wire interval let out between the CTD package & each pump. Pumps were pre-programmed to pump for a certain time interval, and were only retrieved once the time interval had completely passed.

Pumps were deployed with filters placed on “mini-MULVFS” filter holders (see Bishop et al., 2012, L&O Methods and Lam and Morris U.S. patent US 20130298702 A1), which contain 3 sequential filtering platforms for 142-mm diameter filters. When 2 filter pore sizes were used, the smaller pore size filter was placed against a lower frit on the filter holder, and the larger pore size filter was placed on the middle tier. When 3 filter pore sizes were used, all 3 filtering platforms were used, with the largest pore size filter on the top, and the smallest on the bottom frit. On a few occasions where 4 filter pore sizes were used, the two smallest filter pore size were placed together on the bottom platform (frit backing). Filters placed on the middle or top platform in all cases were placed with an additional backing mesh of 150 µm Nitex to maintain material integrity of the filter during flow.

After removal from water, filter holders were detached from pump, carried to an interior lab, and drained gently via vacuum filtration. Filters were removed under laminar flow hood. Samples intended for mercury and thorium analyses were treated using trace-metal clean techniques.

BCO-DMO Processing Notes
 - Generated from original file: "Pump_cast_log_KM1407_KM1418_KM1506.xlsx" contributed by Jeff Drazen
 - Parameter names edited to conform to BCO-DMO naming convention found at Choosing Parameter Name
 - "nd" (no data) inserted into blank cells and cells with "-"
 - Dates reformatted to YYYYMMDD
 - "-" removed from CruiseIds to conform to UNOLS cruiseid convention for the KM
 - "HST_end_time" values for KM1418 Cast PC009 is duration in minutes

Description from NSF award abstract:
The ocean's midwaters are the largest living space on the planet. The mesopelagic food web plays key roles in the biological carbon pump and the production of food for commercially harvested species, but its functioning is understudied because it is remote and technologically challenging to sample. Recent estimates indicate respiratory demand outstrips measured sinking particle supply by up to 2-3 orders of magnitude suggesting that some food inputs to the mesopelagic food web have been underestimated or missed. Suspended particles frequently are not sampled effectively and may be an overlooked food source. Because identifying the principal inputs of organic matter to the deep-sea food web is critical to understanding its function, the investigators propose to evaluate the relative importance of suspended and sinking particles to the meso- and bathypelagic food web in the central North Pacific. They will characterize the isotopic compositions of specific groups of mesopelagic and bathypelagic zooplankton and micronekton, and identify the extent to which they consume suspended or sinking particles using mass balance approaches. The investigators recently have recognized differences in delta 15N and delta 13C values of amino acids (AA) of sinking and suspended particles; these patterns diverge with depth, providing a means to distinguish between food web pathways. The research will define the source-specific isotopic values of suspended and sinking particles at several depths from the surface to the bathypelagic and test proposed microbial mechanisms driving these depth patterns. At corresponding depths, MOCNESS trawls will sample diverse metazoa: zooplankton size fractions, plus targeted resident, migrating and likely suspension-feeding taxa of zooplankton and micronekton. Preliminary data suggest that suspended particles are a secondary food source, containing less labile organic matter than sinking particles that exhibit a seasonal cycle in flux in the central North Pacific. This study will determine if suspended particles become more important to zooplankton and micronekton during a time of year when sinking particle flux is low (Jan/Feb) in comparison to when it is high (Aug), allowing an evaluation of how temporal change in surface ocean productivity affects the functioning of mesopelagic food webs.

Recent research has called for additional study of the ocean's deep midwaters. This study will provide new insights into the functioning of the meso- and bathypelagic food web and its coupling with surface ocean processes in the central North Pacific. The recently-demonstrated ecological tool of amino acid-specific isotopic analysis will provide a novel and comprehensive approach with which to address our hypotheses, and the project will develop the first AA isotopic dataset spanning particles to fish. Results will help identify the ecological underpinnings of increasing delta 15N values with depth in zooplankton -- apparently a common pattern. Zooplankton consumption of suspended particles also could constitute a mechanistic link between the microbial loop and higher trophic levels. The processes controlling the enormous attenuation of particle flux by mesopelagic consumers -- and thereby the strength of carbon sequestration to the deep ocean -- are not understood. Seasonal sampling will help us relate mesopelagic food web processes to changes in surface ocean productivity, furthering our understanding of future climate change impacts on deep-sea food webs and carbon flux. With regard to fisheries, many oceanic top predators such as tuna and swordfish feed on mesopelagic micronekton. A clearer understanding of the structure of mesopelagic food webs will help inform ecosystem models which are used to understand variation in fisheries production.