Cruise Report C-201 : Scientific activities undertaken aboard the SSV Corwith Cramer, Woods Hole, MA – Carriacou, Grenadines - St. Croix USVI, 13 October – 20 November 2005

Woods Hole, MA – Carriacou, Grenadines - St. Croix USVI, 13 October – 20 November 2005This cruise report provides a record of data collected aboard the SSV Corwith Cramer during Cruise C-201 during October and November of 2005. The cruise track transected the North Atlantic Ocean from Woods Hole, MA to St. Croix, USVI (Fig. 1). The sea-going program is an extension of Sea Education Association (SEA) courses conducted for six weeks on shore in Woods Hole and emphasizes the application of theoretical concepts to the study of the oceans. Oceanographic research conducted during Cruise C-201 involved extensive data collection for individual student projects (Table 1) and ongoing SEA research programs. The student projects focused on current scientific problems in physical, chemical, biological, geological, and environmental oceanography, and stressed the interdisciplinary nature of the applied science. In particular, the complex interaction of oceanic processes was emphasized by interdisciplinary, regional, and temporal comparative analyses of the various data sets collected. Student research papers are available on request from SEA. During the cruise, samples or data were collected at 190 discrete oceanographic stations (Tables 2 and 3) in addition to continuously sampling water depth, sub-bottom acoustic profiling, Acoustic Doppler Current Profiles (ADCP) and flow-through sea surface temperature, salinity and in-vivo fluorescence. This report summarizes sea surface chemical properties (Table 3), subsurface physical, chemical and biological characteristics (Fig. 2, Tables 4 and 5), and surface sediment qualities (Table 6). Lengthy CTD, CHIRP, ADCP and flow-through data are not reported here. All unpublished data can be made available by arrangement with the SEA archivist (Contact information, p.2). The information contained in this report is not intended to represent final interpretation of the data and should not be excerpted or cited without written permission from SEA.NS

Cruise Report S-204 : Scientific Activities Undertaken Aboard the SSV Robert C. Seamans, Oahu, HI, USA – Kiritimati, Republic of Kiribati – Palmyra Atoll, USA – Oahu, HI, USA. 24 March – 1 May 2006

Oahu, HI, USA – Kiritimati, Republic of Kiribati – Palmyra Atoll, USA – Oahu, HI, USA. 24 March – 1 May 2006This cruise report provides a record of data collected aboard the SSV Robert C. Seamans during Cruise S-204 during March - May of 2006. The cruise track transected the central Pacific Ocean from Oahu, HI to the Equator and back (Fig. 1). The sea-going program is an extension of Sea Education Association (SEA) courses conducted for six weeks on shore in Woods Hole and emphasizes the application of theoretical concepts to the study of the oceans. Oceanographic research conducted during Cruise S-204 involved extensive data collection for individual student projects (Table 1) and ongoing SEA research programs. The student projects focused on current scientific problems in physical, chemical, biological, geological, and environmental oceanography, and stressed the interdisciplinary nature of the applied science. In particular, the complex interaction of oceanic processes was emphasized by interdisciplinary, regional, and temporal comparative analysis of the various data sets collected. Student research papers are available on request from SEA. Permission to conduct oceanographic research within the territorial jurisdiction of the Republic of Kiribati was most kindly granted by the Ministry of Foreign Affairs and Immigration of the Republic of Kiribati under Diplomatic Note: FA:44/21/060. Water sampling within the Jarvis Island and Palmyra Atoll National Wildlife Refuges was performed under Special Use Permit 12533-06018 under the auspices of the United States Department of Interior, Fish and Wildlife Service. Special thanks to the Project Leader of the Pacific Remote Islands NWR Complex for granting said Permit, and to The Nature Conservancy staff at Palmyra Atoll for hosting such an educationally beneficial port stop. During the cruise, samples or data were collected at 167 discrete oceanographic stations (Tables 2 and 3) in addition to continuously sampling water depth, sub-bottom acoustic profiling, Acoustic Doppler Current Profiles (ADCP) and flow-through sea surface temperature, salinity and in-vivo fluorescence. This report summarizes sea surface chemical properties (Table 3), subsurface physical, chemical and biological characteristics (Fig. 2, Tables 4 and 5), and surface sediment qualities (Table 6). Lengthy CTD, CHIRP, ADCP and flow-through data are not reported here. All unpublished data can be made available by arrangement with the SEA archivist (Contact information, p.2). The information contained in this report is not intended to represent final interpretation of the data and should not be excerpted or cited without written permission from SEA.N.S.F

Cruise Report S-215 : scientific activites undertaken aboard the SSV Robert C. Seamans, Tahiti, French Polynesia – Nuku Hiva, Marquesas, French Polynesia– Oahu, HI, USA, 13 February – 21 March 2008

Tahiti, French Polynesia – Nuku Hiva, Marquesas, French Polynesia– Oahu, HI, USA, 13 February – 21 March 2008This cruise report provides a record of data collected aboard the SSV Robert C. Seamans during Cruise S-215 during February – March of 2008. The cruise track transected the central Pacific Ocean from Tahiti, French Polynesia to Oahu, HI with a port stop at Nuku Hiva, French Polynesia (Fig. 1). The sea-going program is an extension of Sea Education Association (SEA) courses conducted for six weeks on shore in Woods Hole and emphasizes the application of theoretical concepts to the study of the oceans. Oceanographic research conducted during Cruise S-215 involved extensive data collection for individual student projects (Table 1) and ongoing SEA research programs. The student projects focused on current scientific problems in physical, chemical, biological, geological, and environmental oceanography, and stressed the interdisciplinary nature of the applied science. In particular, the complex interaction of oceanic processes was emphasized by interdisciplinary, regional, and temporal comparative analyses of the various data sets collected

The geological record of oceanic crustal accretion and tectonism at slow-spreading ridges

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997.Six folded maps in pocket following text.Includes bibliographical references (leaves 179-182).by Gary Edward Jaroslow.Ph.D

Quantitative analysis of abyssal hills in the Atlantic Ocean : a correlation between inferred crustal thickness and extensional faulting

Author Posting. © American Geophysical Union, 1995. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 100, no. B11 (1995): 22509–22522, doi:10.1029/95JB02510.A recent cruise to the Office of Naval Research Atlantic Natural Laboratory obtained ∼100% Hydrosweep bathymetrie coverage, >200% Hawaii MRl (HMRl) side scan coverage, gravity and magnetics over an area spanning three ridge segments along axis (∼25°25′N to ∼27°10′N), and crustal ages from 0 to 26–30 Ma (∼400 km) on the west flank of the Mid-Atlantic Ridge. This data set represents a first opportunity for an extensive regional analysis of abyssal hill morphology created at a slow spreading ridge. The primary purpose of this work is to investigate the relationship between abyssal hill morphology and the properties of the ridge crest at which they were formed. We apply the method of Goff and Jordan [1988] for the estimation of two-dimensional statistical properties of abyssal hill morphology from the gridded Hydrosweep bathymetry. Important abyssal hill parameters derived from this analysis include root-mean-square (rms) height, characteristic width, and plan view aspect ratio. The analysis is partitioned into two substudies: (1) analysis of near-axis (< 7 Ma) abyssal hills for each of the three segments and (2) analysis of temporal variations (∼2–29 Ma) in abyssal hill morphology along the run of the south segment. The results of this analysis are compared and correlated with analysis of the gravity data and preliminary determination of faulting characteristics based on HMRl side scan data. Principal results of this study are: (1) Abyssal hill morphology within the study region is strongly influenced by the inside-outside corner geometry of the mid-ocean ridge segments; abyssal hills originating at inside corners have larger rms height and characteristic width and smaller plan view aspect ratio than those originating at outside corners. (2) The residual mantle Bouguer gravity anomaly is positively correlated with intersegment and along-flow-line variations in rms height and characteristic width, and it is negatively correlated with plan view aspect ratio. From this result, we infer that lower-relief, narrower, and more elongated abyssal hills are produced when the crust being generated is thicker. (3) Intersegment variations in near-axis rms height negatively correlate with average fault density as determined from analysis of HMRl side scan imagery.This research was supported by the Office of Naval Research under grants N00014-92-J-1214, N00014-94-I-0197, N0014-90-J-1621, and N0014-94-1-0466. G.E.J. was supported by ONR AASERT grant N00014-93-I-1153, and additional support to J.L. was provided by NSF grant OCE93-00708

Influence of Central Pacific Oceanographic Conditions on the Potential Vertical Habitat of Four Tropical Tuna Species

Climate change has resulted in the geographic and vertical expansion of oxygen minimum zones but their impact on the vertical distribution of commercially important species, such as tunas, is not well understood. Although La Nina events are characterized by increased upwelling along the equator, the increased primary productivity and bacterial proliferation drive the expansion of oxygen minimum zones. Vertical habitat of four tropical tuna species were characterized using direct observations of the oceanographic conditions of the Central Pacific Ocean during the 2008 La Nina event and existing primary literature on temperature and dissolved oxygen physiological tolerances for these tunas. Concentrations of potential prey were estimated using Acoustic Doppler Current Profiler raw backscatter and surface zooplankton tows. Based on the oceanographic conditions observed from February to Tune, low dissolved oxygen levels, more so than low temperatures, were inferred to restrict the predicted vertical habitat of four commercially important tuna species (bigeye, yellowfin, skipjack, and albacore). During peak La Nina conditions, temperature and dissolved oxygen tolerance limits of all four tuna species were reached at approximately 200 m. Zooplankton and myctophid fish densities peaked in the upper 200 in between 0 degrees N and 5 degrees N, which corresponded to a region with a shallow thermochne (150 m). Our findings suggest the possibility that competition and susceptibility to surface fishing gears may be increased for tropical tunas during a strong La Nina event due to vertical habitat restrictions

Submersible study of an oceanic megamullion in the central North Atlantic

Author Posting. © American Geophysical Union, 2001. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 106, no. B8 (2001): 16145–16161, doi:10.1029/2001JB000373.Recently discovered megamullions on the seafloor have been interpreted to be the exhumed footwalls of long-lived detachment faults operating near the ends of spreading segments in slow spreading crust. We conducted five submersible dives on one of these features just east of the rift valley in the Mid-Atlantic Ridge at 26°35′N and obtained visual, rock sample, gravity, and heat flow data along a transect from the breakaway zone (where the fault is interpreted to have first nucleated in ∼2.0–2.2 Ma crust) westward to near the termination (∼0.7 Ma). Our observations are consistent with the detachment fault hypothesis and show the following features. In the breakaway zone, faulted and steeply backtilted basaltic blocks suggest rotation above a deeper shear zone; the youngest normal faults in this sequence are interpreted to have evolved into the long-lived detachment fault. In younger crust the interpreted detachment surface rises as monotonously flat seafloor in a pair of broad, gently sloping domes that formed simultaneously along isochrons and are now thinly covered by sediment. The detachment surface is locally littered with basaltic debris that may have been clipped from the hanging wall. The domes coincide with a gravity high that continues along isochrons within the spreading segment. Modeling of on-bottom gravity measurements and recovery of serpentinites imply that mantle rises steeply and is exposed within ∼7 km west of the breakaway but that rocks with intermediate densities prevail farther west. Within ∼5 km of the termination, small volcanic cones appear on the detachment surface, indicating melt input into the footwall. We interpret the megamullion to have developed during a phase of limited magmatism in the spreading segment, with mantle being exhumed by the detachment fault <0.5 m.y. after its initiation. Increasing magmatism may eventually have weakened the lithosphere and facilitated propagation of a rift that terminated slip on the detachment fault progressively between ∼1.3 m.y. and 0.7 m.y. Identifiable but low-amplitude magnetic anomalies over the megamullion indicate that it incorporates a magmatic component. We infer that much of the footwall is composed of variably serpentinized peridotite intruded by plutons and dikes.B. Tucholke's research was supported by NSF grant OCE-9503561 and by an award from the Andrew W. Mellon Foundation Endowed Fund for Innovative Research and the Henry Bryant Bigelow Chair in Oceanography at Woods Hole Oceanographic Institution. G. Hirth acknowledges support by NSF grant OCE-9907244

Thermal structure of oceanic transform faults

Author Posting. © Geological Society of America, 2007. This article is posted here by permission of Geological Society of America for personal use, not for redistribution. The definitive version was published in Geology 35 (2007): 307-310, doi:10.1130/G23112A.1.We use three-dimensional finite element simulations to investigate the temperature structure beneath oceanic transform faults. We show that using a rheology that incorporates brittle weakening of the lithosphere generates a region of enhanced mantle upwelling and elevated temperatures along the transform; the warmest temperatures and thinnest lithosphere are predicted to be near the center of the transform. Previous studies predicted that the mantle beneath oceanic transform faults is anomalously cold relative to adjacent intraplate regions, with the thickest lithosphere located at the center of the transform. These earlier studies used simplified rheologic laws to simulate the behavior of the lithosphere and underlying asthenosphere. We show that the warmer thermal structure predicted by our calculations is directly attributed to the inclusion of a more realistic brittle rheology. This temperature structure is consistent with a wide range of observations from ridge-transform environments, including the depth of seismicity, geochemical anomalies along adjacent ridge segments, and the tendency for long transforms to break into small intratransform spreading centers during changes in plate motion.Funding was provided by National Science Foundation grants EAR-0405709, EAR-0509882, OCE-0548672, and OCE-0623188

Crustal thickness anomalies in the North Atlantic Ocean basin from gravity analysis

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q0AE02, doi:10.1029/2010GC003402.Gravity-derived crustal thickness models were calculated for the North Atlantic Ocean between 76°N and the Chain Fracture Zone and calibrated using seismically determined crustal thickness. About 7% of the ocean crust is 7 km thick and is interpreted to have been affected by excess magmatism. Thin crust probably reflects reduced melt production from relatively cold or refractory mantle at scales of up to hundreds of kilometers along the spreading axis. By far the most prominent thick crust anomaly is associated with Iceland and adjacent areas, which accounts for 57% of total crustal volume in excess of 7 km. Much smaller anomalies include the Azores (8%), Cape Verde Islands (6%), Canary Islands (5%), Madeira (<4%), and New England–Great Meteor Seamount chain (2%), all of which appear to be associated with hot spots. Hot spot–related crustal thickening is largely intermittent, suggesting that melt production is episodic on time scales of tens of millions of years. Thickened crust shows both symmetrical and asymmetrical patterns about the Mid-Atlantic Ridge (MAR) axis, reflecting whether melt anomalies were or were not centered on the MAR axis, respectively. Thickened crust at the Bermuda and Cape Verde rises appears to have been formed by isolated melt anomalies over periods of only ∼20–25 Myr. Crustal thickness anomalies on the African plate generally are larger than those on the North American plate; this most likely results from slower absolute plate speed of the African plate over relatively fixed hot spots.Supported by a fellowship from the China Scholarship Council. Additional support for this research was provided by the Charles D. Hollister Endowed Fund for Support of Innovative Research at WHOI (JL) and NSF China grants 40676023 and 40821062 (YJC)