USGS - science for a changing world

USGS Coastal and Marine Geology Program

Field Activity Details for field activity 2018-602-FA

AKA: Rio Grande Rise (RGR 1), 2018

Other ID: Cruise RGR 1

Status: Completed

Organization(s): USGS, Pacific Coastal and Marine Science Center

Funding Program(s): Pacific EEZ Minerals (ZP00AZ9)

Principal Investigator(s): Kira Mizell, James Hein

Affiliate Investigator(s): Luigi Jovane, University of Sao Paulo, Brazil

Information Specialist(s): James Hein

Data Type(s): Time Series: Mooring (physical oceanography), Sonar: Sound Velocity, Sonar: Sidescan, Sonar: Multibeam, Seismics: Sub Bottom Profiler, Sampling: Geology, Sampling: Chemistry, Sampling: Biology, Location-Elevation: Navigation, Geochemical: Surveys (geochemical), Environmental Data: Temperature, Environmental Data: Sediment Properties, Environmental Data: pH, Environmental Data: Nutrients, Environmental Data: Fluorescence, Environmental Data: Dissolved Oxygen, Environmental Data: Depth, Environmental Data: Density, Environmental Data: Current, Environmental Data: CTD, Environmental Data: Conductivity, Environmental Data: Chlorophyll, Electro-Magnetic: Magnetics, Biological Field Study: Surveys (biological)

Scientific Purpose/Goals: Collect baseline information and samples of ferromanganese crusts and phosphorites from Rio Grande Rise to determine processes mineralization

Vehicle(s): None

Start Port/Location: Port Santos, Brazil

End Port/Location: Port Santos, Brazil

Start Date: 2018-01-26

End Date: 2018-02-24

Equipment Used: instrumentmooring, ADVF, computer, acousticbackscatter, multibeam, subbottomprofiler, 512 chirp-source, samples, Gravity Core, dredge, corer, boxcore, GPS, Other, Nutrient sampler, hydrometer, Sensors - pressure, pressuregauge, flourometer, oxygenprofiler, current meter, acousticdoppler, salinity sensor, Other, temperature, watersamples, CTDmeter, Magnetometer, magnetometer, water bottle

Information to be Derived: sample analysis of marine minerals to understand processes of mineralization

Summary of Activity and Data Gathered: Jim Hein and his PhD student and USGS intern, Kira Mizell, PCMSC, participated in a research cruise from 28 January to 21 February to the Rio Grande Rise in the SW Atlantic Ocean aboard the University of São Paulo (Brazil) ship R/V Alpha Crucis (formally University of Hawaii’s ship, Moana Wave). The goals of the cruise were to better understand this enigmatic plateau and to collect samples to determine the genesis of the mineral deposits and processes of mineralization that have occurred on this flat-topped plateau. We had some ideas about the origin of the mineral deposits, ferromanganese (FeMn) crusts and phosphorite, based on huge slabs Jim saw in a warehouse some years ago collected by CPRM (Geological Survey of Brazil). Unfortunately, the Alpha Crucis did not have the capacity to collect such large samples, but using a variety of 1-meter wide dredges, we were able to collect abundant phosphorite and FeMn crust samples, mostly from the upper parts of the plateau, 600-900 m water depths. Another goal of the cruise was to train Kira, as well as the University of São Paulo researchers and ship’s crew, on dredging logistics and techniques, which they had not done previously, and to provide guidance on the techniques of study and current understanding of the geneses of these types of deep-ocean mineral deposits. Of the 22 days aboard ship, 15 days were packed full with various operations, rock and sediment sampling, multibeam and back-scatter mapping, water-column hydrography and sampling, and laboratory activities, during which Kira and Jim assisted in the completion of 17 dredges that recovered several hundred kilograms of rocks, of which more than 250 rock sample were cut on a diamond saw and described in detail. The rock samples proved very interesting with an amazing variety of phosphorites, FeMn crusts, volcanic rocks, limestones, and others, as well as some very curious rocks, such as granitic gneiss, which should not occur on this plateau; we guess that these rounded pebbles were ice rafted from perhaps Patagonia during the last ice age. The FeMn crusts are particularly unique in that they appear to be heavily phosphatized throughout, and their surfaces are smoothed and polished, indicating that they are not presently growing and that current activity has been vigorous in this region, which eroded the non-phosphatized parts of FeMn crusts found on the flat top of the plateau. In addition, very few of the volcanic rocks were broken from outcrop, which indicates that they were talus debris; follow-up studies using a ROV, cameras, and larger, heavier dredges will be important. This cruise was indispensable as a teaching tool for how to interpret the in situ context of rocks that are recovered by dredge alone and how to proceed with additional studies.

Staff: James Hein, Kira Mizell

Affiliate Staff:

Notes: While in Brazil, post-cruise briefings and lectures were given by Hein at the University of Sao Paulo.

Location:

Rio Grande Rise, SW Atlantic

Boundaries
North: -29.4778612 South: -34.4778612 West: -39.375 East: -29.1015625

Platform(s):

Publications

Portals/Viewers

Data Acquired

Survey EquipmentSurvey InfoData Type(s)Data Collected
instrumentmooring --- Mooring (physical oceanography)
ADVF --- Sound Velocity
computer --- Sidescan
acousticbackscatter --- Sidescan
multibeam --- Multibeam
subbottomprofiler --- Sub Bottom Profiler
512 chirp-source --- Sub Bottom Profiler
samples --- Biology
Chemistry
Geology
Gravity Core --- Geology
dredge --- Geology
corer --- Geology
boxcore --- Geology
Biology
GPS --- Navigation
Other --- --- ---
Nutrient sampler --- Chlorophyll
Nutrients
hydrometer --- Density
Sensors - pressure --- Depth
pressuregauge --- Depth
flourometer --- Fluorescence
oxygenprofiler --- Dissolved Oxygen
current meter --- Current
acousticdoppler --- Current
salinity sensor --- Conductivity
Other --- --- ---
temperature --- Temperature
watersamples --- Conductivity
CTD
Dissolved Oxygen
Fluorescence
Nitrate
pH
Temperature
Turbidity
Wave
CTDmeter --- CTD
Magnetometer --- Magnetics
magnetometer --- Magnetics
water bottle --- Surveys (biological)
Biology
Chemistry

Accessibility FOIA Privacy Policies and Notices

U.S. Department of the Interior | U.S. Geological Survey
Questions or Comments? Contact CMGDS Team
https://cmgds.marine.usgs.gov