ALBERT

Description: The continental shelf off the northeastern coast of the United States was the first of our offshore coastal areas to be charted in detail by the Coast and Geodetic Survey, starting on Georges Bank in 1930. The techniques responsible for this increased accuracy in offshore waters were first described by Rudé (1938) and have been constantly improved. From these soundings Veatch and Smith (1939) compiled their set of contour charts aided by a grant from the Penrose Bequest of the Geological Society of America. These soundings reopened the submarine canyon problem first commented upon by Dana (1863), which had gradually lapsed into obscurity from insuffcient data. The reader is, of course, well aware of the major controversy, with all its far reaching implications, which has been precipitated since the 1930 surveys of Georges Bank were brought to the attention of geologists by Shepard (1933). As more of the new surveys were completed, data from the field sheets were kindly furnished by the U. S. Coast and Geodetic Survey to the Woods Hole Oceanographic Institution for use in dredging and coring operations. This field work, first reported in 1936, was continued from time to time until 1941 as new soundings became available. Rock dredging and coring has been carried out in every major canyon on the slope from Corsair Canyon at the tip of Georges Bank to Norfolk Canyon off the entrance to the Chesapeake (Fig. I). Numerous cores have also been taken from the areas in between; and while the whole slope from Georges to the Chesapeake has not been covered, it is believed that no significant areas have been missed. In fact, cores from the slope taken during the summers of 1940 and 1941 have yielded results that are corroborative rather than new. In 1938 on a cruise from Hudson Gorge to Norfolk Canyon, cores were taken on the slope in areas which Veatch had considered to be the most important (personal communication). In the following report the tows and cores will be described by areas from Georges Bank southwards, as the same region was revisited in successive years. The various samples, however, will be referred to by number followed by the year in which they were taken. The material is in storage in the Woods Hole Oceanographic Institution and in the Museum of Comparative Zoology at Harvard University. The late Joseph A. Cushman was kind enough to identify the Foraminifera which have been obtained in tows from the canyon walls and in cores, except for those described in Appendix A which is contributed by Fred B Phleger, Jr. Most of the type material is in storage in the Museum of Comparative Zoology, although at the present writing some is in the Cushman Laboratory in Sharon, Massachusetts. I am indebted to Lloyd W. Stephenson for identifying a molluscan fauna from one of the canyons, and to W. C. Mansfield who has reported on another formation. Numerous discussions with Percy E. Raymond have, as usual, proved most helpful, and thanks are also due to Eugenia C. Lambert for performing the mechanical analyses and to Constance French for other laboratory assistance. Phleger (1939, 1942, 1946) has previously published on the Foraminifera from the slope and deep water cores. This material is, at present, at Scripps Institution of Oceanography.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June, 1979

Description: A major goal in the study of plate tectonics is the acquisition of a knowledge of the history of relative motion among the rigid plates of the earth's lithosphere. The three papers of this thesis contribute to this effort and demonstrate that studies of the stability and evolution of triple junctions and of the finite rotations of systems of three plates can yield significantly more accurate tectonic histories than can studies of the relative motions between two plates alone. Topographic and magnetic investigation of the Southwest Indian Ridge and reconstruction of the plate system of the Indian Ocean shows that both Africa and Antarctica are rigid plates and their pole of relative rotation has remained fixed near 8°N, 42°W since the Eocene. A detailed survey of the Indian Ocean triple junction reveals that the Indian Ocean plate motions have remained constant since 10 Ma. The stability conditions of the junction show that the general morphology of the Southwest Indian Ridge results from the evolution of the Indian Ocean triple junction. A method is presented for determining the finite rotations best reconstructing the past relative positions of three plates around a triple junction. The method is illustrated by reconstructions of the plates around the Labrador Sea triple junction at the times of anomalies 24 (56 Ma) and 21 (50 Ma). The region of uncertainty of the Greenland-North America finite pole is mapped for each reconstruction, and it demonstrates that consideration of the three plate system yields more well-constrained results than does a treatment of the two plates alone.

Description: This work was supported by the Office of Naval Research contract N00014-75-C-0291 with the Massachusetts Institute of Technology.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution October 1985

Description: The outer continental margin of Nova Scotia is divided by a diapir province, 40-110 km wide and ~1000km long, that trends subparallel to the shelf edge along the upper continental rise and slope. The growth pattern for a small region of this margin (61°-64°W) during the Late Cretaceous and Cenozoic was studied using seismic stratigraphy and well data. Structure maps show that a steep continental slope existed landward of the diapir province (~2200-3800 m water depth) from Early Cretaceous until Miocene time when onlapping upper rise sediments reduced the gradient. Shelf edge canyons were cut during the late Maestrichtian-early Paleocene, Eocene-Oligocene, and Pleistocene. Extensions of Tertiary canyons onto the slope are poorly defined, but small Paleocene fans of interbedded chalk and mudstone on the upper rise indicate that slope canyons existed at that time. Abyssal currents eroded the upper rise and smoothed relief on the continental slope in the Oligocene and middle(?) Miocene. In the Miocene, turbidites may have ponded on the upper rise landward of seafloor highs uplifted by salt ridges or pillows. Pliocene-Pleistocene sediments drape over pre-existing topography. At the beginning and end of the Pleistocene, turbidity currents, caused by delivery of large sediment loads to the shelf edge by glaciers, eroded the present canyon morphology. The late Cenozoic section of the lower continental rise thins seaward from ~2 km near the diapir province and rests on Horizon Au, a prominent unconformity eroded during the Oligocene by abyssal currents. The morphology of the lower rise is largely due to construction by down-slope deposits shed in the Miocene-Pliocene from uplift of the diapir province. Abyssal currents episodically eroded sediment, but current controlled deposition formed only a thin (〈300 m) deposit in the Pliocene(?). Uplift in the diapir province accelerated during the Pleistocene and olistostromes up to 300 m thick were shed onto the lower rise. In the latest Pleistocene, sediments transported down-slope by near-bottom processes accumulated west of a sharp boundary running near 62°30'W from 500 m seaward to the abyssal plain. To the east, hemipelagic sediments accumulated above 4300 m, while turbidity currents, originating in deep canyons to the east, and abyssal currents reworked sediments below 4300 m. A glacial sediment source and relict shelf morphology controlled sedimentation processes and, thus, the location of depocenters on the slope and rise.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution February 1994

Description: This thesis is concerned with understanding how oceanic crust is emplaced at mid-ocean ridges. The emphasis is upon fast-spreading ridges, and the use of seismic techniques to image the uppermost several hundred meters of the crust. We present the results of nine on-bottom seismic refraction experiments carried out over young East Pacific Rise (EPR) crust. The experiments are unusual in that both the source and receiver are located within a few meters of the seafloor, allowing high-resolution determinations of shallow crustal structure. Three experiments were located within the axial summit caldera (ASC), over 'zero-age' crust. The seismic structure at these three locations is fundamentally the same, with a thin (〈60 m) surficial low-velocity (〈2.5 km/s) layer, a 100-150 m thick transition zone with velocities increasing by approximately 2.5 km/s, and a layer with velocities of ~5 km/s at a depth below the seafloor of 130-190 m. The surficial low-velocity layer and transition zone are defined as seismic layer 2A, and the ~5 km/s layer as layer 2B. Both the surficial low-velocity layer and the transition zone double in thickness within ~1 km of the rise axis, with the depth to the 2A/2B boundary increasing from ~150m to 300-350 m over this range. The doubling of layer 2A thickness within 1-2 km of the rise axis is confirmed by multi-channel seismic (MCS) and wide-angle profile (WAP) data, which also indicate that there is no further systematic change in thickness with greater range from the rise axis. Inversions for attenuation structure demonstrate that the layer 2A/2B interface is not only a velocity boundary, but also an attenuation boundary, with Q increasing from 10-20 within layer 2A to 〉70 in layer 2B. The results of MCS and wide-angle experiments over plausible velocity structures are predicted quantitatively, based on velocity models constructed from on-bottom seismic refraction experiments and expanding spread profiles. We conclude that the accuracy of correlating the prominent shallow reflector observed in MCS and WAP data with the layer 2A/2B boundary is strongly dependent on the structure within layer 2A. If layer 2A consists of a surficial low-velocity layer overlying a steep velocity gradient (our gradient model), then there is an excellent correspondence between the two-way travel times to the shallow reflector and the base of layer 2A. However, the shallow reflector may follow structure within layer 2A if the upper crust contains more than one high-gradient region (our step model). A shallow structure similar to the step model is consistent with onbottom refraction experiments and expanding spread profiles located over zero-age EPR crust. With distance from the rise axis, this step-like structure is apparently destroyed, and is converted into a single steep gradient similar in appearance to our gradient model. Layer 2A is interpreted to be composed of the extrusive section and transition zone, with layer 2B consisting of the sheeted dike complex. This implies that the top of the dikes subsides from 150-200 m to 250-450 m within 1-2 km of the rise axis, and then remains at a relatively constant depth beneath the seafloor. The thickening of the extrusive layer is interpreted to be due to lava that either overflows the ASC walls, is emplaced through eruptions outside of the ASC, or travels laterally from the ASC through subseafloor conduits. Off-axis sill emplacement also contributes to the thickening of layer 2A. According to this model, the shallow crustal architecture is in place within 1-2 km of the rise axis. We suggest that the process of dike subsidence is controlled by the axial magma chamber (AMC), which we define as the melt lens and underlying mush zone. Within the neovolcanic zone, buoyancy forces associated with the AMC are supporting the extrusive layer and sheeted dikes. With distance from the rise axis, the AMC solidifies, the crust cools, the buoyancy forces are reduced, and the sheeted dike complex subsides. Concurrently, the extrusive layer thickens resulting in significantly less subsidence of the seafloor. The primary implication of this model is that dikes will subside to a greater depth for a robust magma chamber than for a weak magma chamber. A prominent deval is located at latitude 9°35'N, and this is coincident with our observations of a 50% decrease in dike subsidence as determined from MCS, WAP, conventional airgun refraction, and tomography data. Our subsidence model would predict that a relatively weak magma chamber is located at 9°35'N. A low magma supply at the devallocation is compatible with tomography and MCS seismic data. The decrease in layer 2A thickness suggests that the localized region of low magma supply has persisted for 175,000-275,000 years. Knowledge of shallow crustal structure is the key to understanding emplacement processes at mid-ocean ridges. Seismic studies at the fast-spreading East Pacific Rise indicate that each technique has advantages and disadvantages. On-bottom seismic refraction experiments can provide high-resolution determinations of upper crustal velocities, but only for limited areas. Conventional airgun refraction studies can extend the velocity structure to a larger region, at the expense of resolution. Multi-channel seismic and wide-angle profile data can map horizons in the shallow crust over large areas, but require good velocity information to be properly interpreted. Future work can ground truth seismic observations with observed lithology, and expand our knowledge of emplacement processes to intermediate-spreading and slow-spreading ridges.

Description: The work in this thesis was supported by the Office of Naval Research, a National Science Foundation graduate student fellowship, and grant OCE-8917750 from the National Science Foundation.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1995

Description: The global mid-ocean ridge system is one of the most striking geological features on the surface of the Earth. In this system, the East Pacific Rise (EPR) is the fastest spreading ridge and is thus considered as the most active magmatically among the plate boundaries. In January and February of 1988, an extensive survey by the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution was conducted along the EPR between 9°05' and 9°55'N to study the crustal structure of the axial region. This thesis, the result of that cruise, comprises four main topics: (1) characterization of normal faulting from Sea Beam bathymetric data, (2) application of mechanical models to explore the hypothesis that buoyancy arising from crustal magma chambers and gravitational spreading of the upper crust are the principal processes leading to the initiation and development of normal faults, (3) investigation of seafloor magnetization anomalies to constrain upper crustal structure, and (4) analysis of gravity anomalies to examine possible correlations between observed variations in seafloor manifestations of volcanism and deformation and underlying structure. Thus, each topic focuses on different levels of the mid-ocean ridge. Together with the results of seismic and other observations, the findings are woven into a better understanding of the tectonic processes and structure of fastspreading mid-ocean ridges. First, to understand the characteristics of normal faults at fast-spreading ridges, we utilized swaths of Sea Beam bathymetry and estimated the distribution and geometry of normal fault zones using the slope of the seafloor as the criterion for a faulted surface. In our survey area, nonnal fault activity begins 2-8 km off-axis and continues at least to 30-40 km from the axis, as indicated by an increase in the total and average throws of normal fault zones versus distance from the axis. There appears to be no significant difference in the plan-view area of inward- and outward-facing nonnal fault zones. The distance from the rise axis to the nearest large-offset fault zone (throw 〉 20 m) on either side of the axis is approximately symmetric to the north of 9°23'N, but the midpoint between nearest largeoffset fault zones is offset 2-3 km to the west of the bathymetric axis to the south of 9°23'N. The continued growth of nonnal fault zones suggests that significant extensional stress persists to greater distances from the axis than previously thought and that the rise axis possesses a finite strength. The argument that the rise axis has finite strength is consistent with recent evidence for solidified axial dikes along magmatically active portions of the EPR from near-bottom seismic refraction experiments, which suggests that, while eruption of magma at the rise axis weakens the axis, the persistence of such weak zones is short-lived and the emplacement zones at any given time are localized along the axis. We examined how the presence of a low-density, low-strength magma chamber within the crust and gravitational spreading of a mechanically strong upper crust over an underlying substrate contribute to the fonnation of faults at a fast spreading mid-ocean ridge by comparing the predicted stress field with the observed pattern of normal fault zones. We employed boundary element methods to incorporate buoyancy and gravitational spreading as body forces in an elastic medium, and we detennined stress and strain fields for a variety of rise axis conditions and a range of possible sets of material properties for different parts of the mid-ocean ridge. Our results show that the strength of the rise axis is one of the most crucial factors governing the near-axis stress field. If the rise axis is mechanically weak, the maximum extensional stress from buoyancy occurs at shallow depth off the rise axis. A weak rise axis may result from recent magmatism such as the intrusion of dikes into the upper crust. On the other hand, if the rise axis is mechanically strong, which may result after solidification and cooling of the dike zone, the maximum surface extensional stress occurs on the rise axis. However, the reduction in size of a magma chamber that would accompany cessation of dike injection would lead to less buoyancy and thus a lower likelihood of stress levels sufficient for faulting. For a given set of material strengths and a given magnitude of buoyancy force, the flexural rigidity of the upper crust plays an important role in detennining if a zone of extension will develop off axis and, if so, the position and horizontal extent of that zone. A thin or mechanically weak upper crust is more likely to develop a zone of extension than one that is thick or mechanically strong. The stress field resulting from gravitational spreading is similarly affected by the strength of the rise axis. While buoyancy can explain a consistent distance at which normal faults initiate off-axis, gravitational spreading can account for continued activity on normal faults to a greater distance from the axis than can buoyancy. The existence of a magma lens can play an important role in reducing the magnitude of the stress field for a weak rise axis, as the crust above the magma lens can slide and thus relieve the thickness-averaged extensional stress. Next, we inverted surface ship measurements of the scalar magnetic field along the EPR between 9°10' and 9°50'N. We examined whether the axial magnetization high, which increases in amplitude to the south in our area, can best be explained by variations in the thickness or in the magnetization intensity of the source layer. The variation in axial magnetization is too large to be explained solely by the variations in the depth to the top of the axial magma chamber indicated by reflection seismology. For a magnetic source layer that is 500 or 750 m thick, the observed along-axis variations in FeO and Ti02 explain only 36 and 60%, respectively, of the total variance of axial magnetization anomalies. Therefore, a combination of variations in magnetic layer thickness and in intensity of magnetization (by variations in the FeO and Ti02 contents of the source rock or by other mechanisms) is needed to explain the along-axis variation of axial magnetization. In addition to the increase in amplitude to the south, the axial magnetization high exhibits at least three marked changes in magnitude and offsets in its along-axis linearity ('magnetic devals') (at 9°25', 9°37', and 9°45'N) which appear to be related to boundaries or offsets between the segments of the axial summit caldera (ASC). Because the amplitudes of the axial magnetization anomalies are highest at the midpoints of the ASC segments, we speculate that midpoints of the ASC segments are the loci of more frequent lava eruptions, and the seafloor basalts at the midpoints are thus younger and more magnetic, than at the segment ends. The magnetization shows distinct short-wavelength (~ 5 km) banding to the north of 9°25'N over a region that does not appear to have been affected by an overlapping spreading center. Among the possible explanations for these off-axis magnetization anomalies are short geomagnetic reversal events within the Brunhes epoch, variations in the paleointensity of the Earth's field, variations in the magnetization intensity of the source rock due to variability in the magmatic supply, and variations in the degree of hydrothermal alteration at the rise axis. On the basis of comparisons of forward models and observations, short geomagnetic reversal events appear to be the most likely explanation of these anomalies. The analysis of sea-surface gravity field measurements shows an axial residual mantle Bouguer gravity anomaly too large to be explained by the anomalous temperature of the mantle or by changes in the thickness of the crust. The broad axial residual gravity low is interpreted as a signal arising largely from the upper mantle, presumably by presence of partial melt along the rise axis. A northward increase in the width of the low implies a greater melt fraction in the region to the north than to the south, especially on the Pacific plate side. The residual gravity anomaly also shows several short-wavelength local lows along the axis (e.g., 9°21', 9°32', and 9°42'N) which correlate with along-axis variations in axial magnetization and tomographic images of mid-crustal seismic velocities. Along axis the local lows have an amplitude of 1.5-3 mGal and appear at a nearly regular spacing (10- 15 km). Across the axis, however, the local lows show a greater variation (3-5 mGal), suggesting that there is an additional gravity anomaly signal arising from a low-density structure that is approximately continuous along the axis. The anomalous masses producing the local lows are interpreted as zones of relatively high melt concentration, formed within the crust by recent replenishment of magma from the upper mantle, that are surrounded by a region of lesser melt concentration corresponding to the low-velocity volume imaged by seismic tomography. If the zone of high melt concentration are modeled as circular rods of radius 1 km, along-axis length 10 km, and center of mass 2.25 km below the seafloor, density contrasts of 200-350 kg/m3 are needed to match the observed anomalies. For larger anomalous mass volumes, the density contrasts would be lower. The findings of this study support the hypothesis that the axis of the EPR can be divided into segments 10-15 km in length, with each segment defmed by the locus and timing of most recent emplacement of magma in the axial crust. The segments in the study area appear to be in different phases of a magmatic cycle, but the period of such a magmatic cycle is not known. By this view, the discrete emplacement of magma bodies gives rise to along-axis variations in crustal structure manifested as short-wavelength residual gravity anomalies and magnetic devals. Another consequence of a rise axis at which magma is emplaced at discrete locations is that the mechanical strength of the axial upper crust varies with position along the axis and over time. During active magmatism, the rise axis acts as a weak zone and the buoyancy of the axial magma chamber and surrounding low-velocity volume can lead to initiation of off-axis normal faulting. However, for a long segment of the rise bounded by transform faults, the axis will have sections with a solidified rucial injection zone as well as sections undergoing active magmatism, and thus the rise overall may appear to have finite strength. If such a finitestrength ridge axis is subject to significant extensional stress as a result of gravitational spreading, mantle convective tractions, or differential cooling, then continued normal fault activity would extend over a broad region to distances of at least several tens of kilometers from the spreading axis.

Description: The work in this thesis was supported by the National Science Foundation under grants OCE-8615797, OCE-8615892, and OCE-9000177.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1996

Description: The objective of this Thesis was to interpret the structural development of slowspreading ridge segments by: 1) delineating the nature, magnitude, and relative importance of primary tectonic and volcanic processes that control crustal morphology, 2) investigating the spatial and temporal variability of these processes, and 3) examining how rheological variations in the lithosphere control its structural configuration. To that end, this Thesis provides detailed documentation of faults and volcanoes (seamounts) at the Mid-Atlantic Ridge from 25°25'N to 27°10'N and extending from zero-age crust at the ridge axis to -29 Ma crust on the ridge flank. This information was used to analyze the evolution of ocean crust from initial formation in the rift valley to degradation by aging processes on the ridge flank. Accumulation of sediments affects the seafloor morphological expression of ocean crustal structure, and sediment thicknesses were also mapped to facilitate study of the morphological record of crustal accretion and tectonism. In addition, deformation conditions in the lithosphere were analyzed by study of microstructure and geothermometry of abyssal peridotite mylonites recovered from fault zones at slow-spreading ridges.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990

Description: As a primary feature of ocean circulation and a key component of the global carbon cycle, changes in the thermocline must be accounted for if we are to understand the processes involved in Quaternary climatic fluctuation. Toward this goal, this thesis contains studies of the modern and glacial thermoclines at the Bahama Banks and it presents an novel approach to determine sea level based on the flux of 230Th and 231Pa from thermocline waters to the seafloor. In the first chapter, the hydrography of the modern thermocline in Northwest and Northeast Providence Channels, Bahamas, is investigated using CTD data. Potential temperature- salinity relationships demonstrate that the deep waters and most of the thermocline waters in these channels originates in the Sargasso Sea. Cross channel sections of water properties suggest the following: (1) water from the shallow core of the Deep Western Boundary Current (Fine and Molinari, 1988) may circulate along the channel margins, and (2) where the western end of Northwest Providence Channel opens to the Florida Straits, shallow flow is toward the straits in the southern portion of the channel and away from the straits in the northern portion. In the next two chapters, changes in the temperature and nutrient structures of the thermocline from the last glaciation to the recent Holocene are inferred from isotopic variations of the planktonic foraminifera Globigerinoides ruber (212-250μm) and G. sacculifer (300-350μm) and the benthic foraminifera Planulina wuellerstorfi, P. ariminensis, P. foveolata and Cibicidoides pachyderma (〉250μm) in a suite of cores from the margins of Little and Great Bahama Banks. During the last glaciation, δ18O values were from 1.4 to 1.9 per mil greater than during the recent Holocene. Based on the δ18O/sea-level model of Fairbanks (1989), we estimate that the upper 1500 m of the water column was cooler by at least 1°C- the deepest waters were several degrees cooler. The temperature gradient (dT/dz) was steeper and the base of the thermocline appears to have stayed at about the same depth or risen slightly. At all depths in the thermocline, δ13C was greater during the last glaciation than during the recent Holocene by at least 0.1-0.2 per mil and as much as 0.6 per mil in the lower thermocline. While recent Holocene δ13C reaches minimum values in the lower thermocline (the poorly-ventilated oxygen minimum/phosphate maximum layer), this feature was not present during the last glaciation. These data show that the concentrations of nutrients throughout the thermocline were reduced and that there was no oxygen minimum layer, indicating greater, more uniform ventilation of thermocline waters. These results are consistent with our understanding of the physics of thermocline circulation and evidence for hydrographic conditions at the ocean surface during the last glaciation, indicating a direct response of thermocline circulation to changes in climate. Cooler thermocline waters reflect cooler surface ocean temperatures at mid-latitudes where thermocline isopycnal surfaces outcrop. Increased, more uniform ventilation of the glacial thermocline is consistent with both more vigorous glacial winds leading to increased Ekman pumping and all isopycnal surfaces of the thermocline outcropping in the area of Ekman downwelling. Taken together with previous studies of intermediate-depth waters, these data document that the entire upper water column of the North Atlantic was depleted in nutrients during the last glaciation. A final suggestion of the third study is that Mediterranean and southern source waters contributed little to deeper intermediate-depth waters in the North Atlantic. The fourth chapter presents two new approaches to reconstruct the sea-level history based on the fluxes of 230Th and 231Pa to the seafloor. The approaches rely on the fact that fluxes of these nuclides to a site on the seafloor are proportional to the height of the water column above the site. Consequently, a change in sea level causes changes in the 230Th and 231Pa fluxes which, at shallow sites, are large fractions of the total fluxes. Past sea level can be reconstructed using either the record of nuclide accumulation in a single core of sediment, or nuclide concentrations in synchronously deposited sediment samples from cores collected over a range of water depths. Importantly, this record of sea level is both continuous (not just high stands) and independent of the assumptions of constant seawater temperature or uplift rate required by some other approaches.

Description: This work was supported by NSF grant number OCE-8813307 to W. Curry, NSF grant number OCE-8800693 to J. Broda and W. Curry and the Education Office of the MIT/WHOI Joint Program in Oceanography.