Table of Contents

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

Thorium isotope data summaries from AMLR and NBP cruises to the Antarctic in 2006

Particulate organic Carbon (POC) flux was determined through measuring Thorium (234Th) reported in dpm/kg .
 

Cruises

AMLR (Antarctic Marine Living Resources) R/V Yuzhmorgeologiya Jan2006:
The research program was focused in the southern Drake Passage
along the Shackelton Shelf located near the Bransfield Strait.
Samples were obtained from the R/V Yuzhmorgeologiya and inflatables
that were taken to island locations.
Lat/Lon Bounding Box
-62.2538Lat, -62.9966Lon
-63.2335Lat, -59.0332Lon
-59.9964Lat, -55.7612Lon
-61.4995Lat, -53.9996Lon

NBP (Nathaniel B. Palmer) R/V Nathaniel B. Palmer July2006:
The research was conducted in the same region of the Drake Passage as the AMLR cruise.
Samples were obtained aboard the R/V Nathaniel B. Palmer
Lat/Lon bounding box
-60.4991Lat, -58.5613Lon
-62.3599Lat, -58.0392Lon
-60.2783Lat, -57.4509Lon
-61.2683Lat, -54.2852Lon
 

Associated Publications

Brzezinski, M.A., Nelson, D.M., Franck, V.M. and Sigmon, D.E., 2001. "Silicon dynamics within an intense open-ocean diatom bloom in the pacific sector of the southern ocean." Deep-Sea Research Part II 48, pp. 3997-4018

Michiel Rutgers van der Loeff, Manmohan M. Sarin, Mark Baskaran, Claudia Benitez-Nelson, Ken O. Buesseler, Matt Charette, Minhan Dai, Örjan Gustafsson, Pere Masque, Paul J. Morris, Kent Orlandini, Alessia Rodriguez y Baena, Nicolas Savoye, Sabine Schmidt, Robert Turnewitsch, Ingrid Vöge, James T. Waples. "A review of present techniques and methodological advances in analyzing 234Th in aquatic systems" Marine Chemistry, Volume 100, Issues 3-4, 1 August 2006, Pages 190-212

Pike, S.M., K.O. Buesseler, J. Andrews and N. Savoye, 2005. "Quantification of 234Th recovery in small volume sea water samples by inductively coupled plasma mass spectrometry." (PDF) Journal of Radioanalytical and Nuclear Chemistry, 263(2): 355-360.

Willard S. Moore and Ralph Arnold (1996). "Measurement of 223Ra and 224Ra in coastal waters using a delayed coincidence counter." Journal of Geophysical Research, vol. 101, no. c1, pages 1321-1329, January 15, 1996.

Sampling and Analytical Methodology

Particle sinking rates were determined using the 4 liter measurement of 234Th (Pike et al., 2005). Samples were collected from hydrocasts from a shipboard CTD. The unfiltered 4-liter samples were immediately acidified to pH ~1.5 using concentrated Nitric acid. Samples were shaken vigorously and 230Th added as a yield monitor. The samples were shaken again and allowed to equilibrate for 8 hours. Concentrated NH4OH was subsequently added to each sample to adjust the pH to 8. Extraction of thorium from seawater was then accomplished by co-precipitation via a MnO2 precipitate onto a 25-mm-diameter QMA filter. The filtered samples were air dried and counted on a RISO beta detector (Rutgers van der Loeff et al., 2006). All samples were counted for at least 24 hours or until the counting error was < 3%. Samples were recounted after >150 days (~6 half lives) to determine the sample background. Detector calibration was confirmed with 3000m deep water sample.

Particulate carbon was collected through a McLane WTS-LV in-situ pump and filtered through a 142mm GFF filter. 22mm subsamples were collected, dried and transported back to the WHOI laboratory for CHN analysis on the Flash EA1112. The samples were pelletized in ultra clean tin capsules, combusted at 900oC, separated in a gas chromatographic column, and measured through a thermal conductivity detector. The CHN analyzer was calibrated by using an acetanilide standard. A second subsample was taken and analyzed for biogenic silica (Brzezinski et al 2001). Sodium Hydroxide was added to the filter and heated to 95oC for 45minutes. It was placed on ice and neutralized with hydrochloric acid. After centrifuging, the supernatant is then analyzed for silicate on a Lachat Quickchem 8000.
 

Data Processing

CHN: Linear regression of standards is used to determine the carbon content of the sample

Th: Thorium is measured using the Riso betacounters. Results published include removal ofsample background, detector efficiency correction, correction of radioactive decay, and chemistry efficiency through analysis of tracer (230Th).

Modifications to original data made to conform to BCO-DMO database convention

Cruise_ID added
Spaces in Sample_ID replaced with dashes for consistency with Radium summary data empty cells filled with "nd" (no data)
Latitude/Longitude headers converted to lat/lon
date reformatted to YYYYMMDD
time reformatted to HHMM
decimal data values padded to consistent decimal places
spaces, minus signs, and "<"'s replaced with underscores or text in misc data headers
POC/PON used in place of Part Organic Carbon/Nitrogen in headers
"No Sample" values replaced with "nd" in Sample_Ids FA-494, FA-495
"Surface" values in Depth data replaced with "1"

Collaborative Research: Plankton Community Structure and Iron Distribution in the
Southern Drake Passage and Scotia Sea

The Shackleton Fracture Zone (SFZ) in Drake Passage of the Southern Ocean defines a
boundary between low and high phytoplankton waters. Low chlorophyll water flowing
through the southern Drake Passage emerges as high chlorophyll water to the east,
and recent evidence indicates that the Southern Antarctic Circumpolar Current Front
(SACCF) is steered south of the SFZ onto the Antarctic Peninsula shelf where mixing
between the water types occurs. The mixed water is then advected off-shelf with
elevatediron and phytoplankton biomass.

The SFZ is therefore an ideal natural laboratory to improve the understanding of
plankton community responses to natural iron fertilization, and how these processes
influence export of organic carbon to the ocean interior. The bathymetry of the region
is hypothesized to influence mesoscale circulation and transport of iron, leading to
the observed patterns in phytoplankton biomass.

The position of the Antarctic Circumpolar Current (ACC) is further hypothesized to
influence the magnitude of the flow of ACC water onto the peninsula shelf, mediating
the amount of iron transported into the Scotia Sea. To address these hypotheses, a
research cruise will be conducted near the SFZ and to the east in the southern Scotia
Sea. A mesoscale station grid for vertical profiles, water sampling, and bottle incubation
enrichment experiments will complement rapid surface surveys of chemical, plankton, and
hydrographic properties. Distributions of manganese, aluminum and radium isotopes will
be determined to trace iron sources and estimate mixing rates.

Phytoplankton and bacterial physiological states (including responses to iron enrichment)
and the structure of the plankton communities will be studied. The primary goal is to
better understand how plankton productivity, community structure and export production
in the Southern Ocean are affected by the coupling between bathymetry, mesoscale circulation,
and distributions of limiting nutrients. The proposed work represents an interdisciplinary
approach to address the fundamental physical, chemical and biological processes that
contribute to the abrupt transition in chl-a which occurs near the SFZ. Given recent
indications that the Southern Ocean is warming, it is important to advance the understanding
of conditions that regulate the present ecosystem structure in order to predict the effects
of climate variability. This project will promote training and learning across a broad
spectrum of groups. Funds are included to support postdocs, graduate students, and
undergraduates. In addition, this project will contribute to the development of content
for the Polar Science Station website, which has been a resource since 2001 for instructors
and students in adult education, home schooling, tribal schools, corrections education,
family literacy programs, and the general public.

Radium and Thorium isotope data summaries from AMLR and NBP cruises to the Antarctic in 2006

Naturally occurring radium isotopes (224Ra, 226Ra, 228Ra) were used in determining
lateral mixing processes which are reported in dpm/m3.

Particulate organic Carbon (POC) flux was determined through measuring Thorium (234Th) reported in dpm/kg.

Cruises

AMLR (Antarctic Marine Living Resources) R/V Yuzhmorgeologiya Jan/2006:
The research program was focused in the southern Drake Passage
along the Shackelton Shelf located near the Bransfield Strait.
Samples were obtained from the R/V Yuzhmorgeologiya and inflatables
that were taken to island locations.
Lat/Lon Bounding Box
-62.2538Lat, -62.9966Lon
-63.2335Lat, -59.0332Lon
-59.9964Lat, -55.7612Lon
-61.4995Lat, -53.9996Lon

NBP (Nathaniel B. Palmer) R/V Nathaniel B. Palmer July/2006:
The research was conducted in the same region of the Drake Passage as the AMLR cruise.
Samples were obtained aboard the R/V Nathaniel B. Palmer
Lat/Lon bounding box
-60.4991Lat, -58.5613Lon
-62.3599Lat, -58.0392Lon
-60.2783Lat, -57.4509Lon
-61.2683Lat, -54.2852Lon

NASA GCMD Link: NASA GCMD

NSF Proposal Title: Collaborative Research: Plankton Community Structure and Iron Distribution in the Southern Drake Passage and Scotia Sea

The Shackleton Fracture Zone (SFZ) in Drake Passage of the Southern Ocean defines a boundary between low and high phytoplankton waters. Low chlorophyll water flowing through the southern Drake Passage emerges as high chlorophyll water to the east, and recent evidence indicates that the Southern Antarctic Circumpolar Current Front (SACCF) is steered south of the SFZ onto the Antarctic Peninsula shelf where mixing between the water types occurs. The mixed water is then advected off-shelf with elevated iron and phytoplankton biomass. The SFZ is therefore an ideal natural laboratory to improve the understanding of plankton community responses to natural iron fertilization, and how these processes influence export of organic carbon to the ocean interior. The bathymetry of the region is hypothesized to influence mesoscale circulation and transport of iron, leading to the observed patterns in phytoplankton biomass. The position of the Antarctic Circumpolar Current (ACC) is further hypothesized to influence the magnitude of the flow of ACC water onto the peninsula shelf, mediating the amount of iron transported into the Scotia Sea. To address these hypotheses, a research cruise will be conducted near the SFZ and to the east in the southern Scotia Sea. A mesoscale station grid for vertical profiles, water sampling, and bottle incubation enrichment experiments will complement rapid surface surveys of chemical, plankton, and hydrographic properties. Distributions of manganese, aluminum and radium isotopes will be determined to trace iron sources and estimate mixing rates. Phytoplankton and bacterial physiological states (including responses to iron enrichment) and the structure of the plankton communities will be studied. The primary goal is to better understand how plankton productivity, community structure and export production in the Southern Ocean are affected by the coupling between bathymetry, mesoscale circulation, and distributions of limiting nutrients. The proposed work represents an interdisciplinary approach to address the fundamental physical, chemical and biological processes that contribute to the abrupt transition in chl-a which occurs near the SFZ. Given recent indications that the Southern Ocean is warming, it is important to advance the understanding of conditions that regulate the present ecosystem structure in order to predict the effects of climate variability. This project will promote training and learning across a broad spectrum of groups. Funds are included to support postdocs, graduate students, and undergraduates. In addition, this project will contribute to the development of content for the Polar Science Station website, which has been a resource since 2001 for instructors and students in adult education, home schooling, tribal schools, corrections education, family literacy programs, and the general public.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

Hewes, C. D., Reiss, C.S., .Kahru, M. , Mitchell, B.G. , and Holm-Hansen, O.. "Control of phytoplankton biomass by dilution and mixed layer depth in the western Weddell-Scotia Confluence (WSC)," Marine Ecology Progress Series, v.366, 2008, p. 15.

Hiscock, M. , Lance, V. , Apprill, A., Bidigare, R , Mitchell, B., Smith Jr. W., Barber, R.. "Photosynthetic maximum quantum yield increases are an essential component of the Southern Ocean phytoplankton response to iron," Proceedings of the National Academy of Sciences, v.105(2), 2008, p. 4775.

Holm-Hansen, O., Kahru, M., Hewes, C.. "Deep chlorophyll a maxima (DCMs) in pelagic Antarctic waters. II. Relation to bathymetric features and dissolved iron concentrations," Marine Ecology-Progress Series, v.297, 2005, p. 71.

Hopkinson, B., Mitchell, B. G., Reynolds, R. A., Wang, H., Selph, K., Measures, C., Hewes, C., Holm-Hansen, O., Barbeau, K.. "Iron limitation Across Chlorophyll Gradients in the Southern Drake Passage: Phytoplankton Responses to Iron Addition and Photosynthetic Indicators of Iron Stress," Limnology and Oceanography, 2007, p. 2540.

Hopkinson, B., Mitchell, B. G., Reynolds, R. A., Wang, H., Selph, K., Measures, C., Hewes, C., Holm-Hansen, O., Barbeau, K.. "Iron limitation Across Chlorophyll Gradients in the Southern Drake Passage: Phytoplankton Responses to Iron Addition and Photosynthetic Indicators of Iron Stress," Limnology and Oceanography, v.52, 2007, p. 2540.

Kahru, M., Mitchell, B. G., Gille, S. T., Hewes, C. D. and Holm-Hansen, O.. "Eddies enhance biological production in the Weddell-Scotia Confluence of the Southern Ocean," Geophys. Res. Let., 34,, v.24, 2007, p. L14603.