A phytoplankton bloom dominated by the pennate diatom Nitzschia curta (Van Heurck) Hasle was observed during January-February 1983 at a receding ice-edge in the Western Ross Sea, Antarctica. The core of the bloom was found between 100-150 Km from the ice-edge. Nitzschia curta cell densities up to 22 x 10⁶ cells/1 were observed. The nanoplankton contributed to 18% (average) of the total biomass. The contribution of another pennate diatom, Nitzschia closterium (Ehrenberg) W. Smith, was significant in two offshore stations (22% and 90%). Other diatom species, dinoflagellates and other phytoplankton groups were very few in number. A wind-driven upwelling event occurred along the ice-edge. The presence of off-shore species (e.g. Nitzschia kerguelensis) close to the ice suggests the existence of an eddy circulation. Results of elemental composition experiments with 10 Antarctic diatoms showed that the C:Si:N ratio for Antarctic diatoms, when compared to the Redfield-Richards ratio for diatoms of other environments, have less carbon and more silicon per unit nitrogen. Comparison of laboratory results with the field data confirms the anomalous elemental composition of the major bloom species observed in the Ross Sea. Blooms like the one observed in this study seem to be restricted to the Western part of the Ross Sea and appear to be produced in inshore waters late in the austral summer. / Graduation date: 1985

A new high-resolution climatology and volumetric θ-S census (Δθ = 0.1°C, ΔS = 0.01) is constructed for the Ross Sea. Property maps (potential temperature, salinity, and dissolved oxygen) along 40 depth levels and 21 neutral density (γn) surfaces are analyzed. A major inflow of Antarctic Surface Water (AASW) is observed branching off the westward-flowing coastal current near Cape Colbeck. One portion continues poleward hugging the coast while the other follows the shelf break to the west. The characteristic “V” shape of the Antarctic Slope Front over the western Ross Sea is indicated by a narrow stream of thickened AASW. The entire AASW layer shoals from east to west. Two major shoreward inflows of Lower Circumpolar Deep Water (LCDW) are inferred. A warm and salty tongue from the Balleny Gyre enters the Drygalski and Joides troughs. A similar tongue is exported from the Ross Gyre and enters the Glomar Challenger Trough. No significant LCDW inflow is observed over the eastern slope of the Ross Sea. The thickest outflows of Shelf Water (SW: θ ≤ -1.85°C, S > 34.5) and new Antarctic Bottom Water (AABW: θ > -1.85°C, γn > 28.27 kg m-3) are found along the Drygalski and Joides troughs. Their saltiest (S > 34.7) components are concentrated in the western Ross Sea, whereas the low-salinity varieties are found throughout the Ross Sea shelf. The most voluminous water mass in the Ross Sea is LCDW. The least abundant is AABW found primarily over the western slope. Modified CDW (MCDW) in the western Ross is inferred to be a mixture of 30% AASW and 70% LCDW; whereas central (eastern) MCDW is 40% (60%) AASW and 60% (40%) LCDW. The same water mass composition is inferred for new AABW in the western and central Ross Sea: 25% SW and 75% MCDW. A 40-year freshening trend is detected at different sites along the coastal transit of AASW from Cape Colbeck to Ross Island. In addition to a freshening, the MCDW and high-salinity SW also reveal a cooling trend. Conversely, a warming and salinification is indicated at the main inflows of LCDW.

Thesis (Ph. D.) -- Lincoln University, 2010. / Also available via the World Wide Web.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / With the goal of determining ice sheet history in the central Ross Sea since the late Miocene, the provenance of glacial till from IODP expedition 374 site U1522 was assessed using a suite of three analyses. A total of 3,869 zircons, between 250-63 microns in size, from sixteen different cores were measured for U-Pb isotopes via LA-ICP-MS. Zircon data was compared to neodymium isotope and clast lithology datasets from collaborators. Site U1522 shows three distinct provenance shifts from the late Miocene to the Pleistocene, two of which are coincident with Ross Sea Unconformities three and two. Late Miocene samples have abundant Cretaceous zircon populations, radiogenic neodymium values, and clasts interpreted as having a West Antarctic provenance. In latest Miocene samples, zircons are mostly Ross Orogeny age (c. 470 615 Ma) and Cretaceous zircon grains are almost absent, neodymium values are relatively un radiogenic, and dolerite clasts are present signaling a shift to East Antarctic derived ice. Above Ross Sea Unconformity 3, early to mid Pliocene samples show a shift back to West Antarctic provenance with abundant Cretaceous zircons and more radiogenic neodymium values. Late Pliocene to Pleistocene samples, deposited above Ross Sea Unconformity 2, reflect dominant East Antarctic provenance with few Cretaceous zircon dates, relatively un radiogenic neodymium values, and the presence of dolerite clasts. These data are broadly in agreement with ice sheet interpretations suggested by clast analysis from ANDRILL site AND-1B. Permo-Triassic zircon dates suggest the presence of unexposed bedrock of this age beneath the West Antarctic Ice Sheet based on their association with Cretaceous dates that have not been reported from East Antarctica. The zircon dataset also reveals two late Miocene intervals with a previously undocumented Eocene Oligocene magmatic event ~30 40 Ma. The coexistence of Cretaceous dates in these intervals suggests a likely West Antarctic source. The absence of Eocene Oligocene zircons in subsequent Plio Pleistocene sediments may be explained by substantial erosion and offshore deposition of the West Antarctic interior, including volcanic edifices following the Middle Miocene Climatic Transition.

A marginal ice zone (MIZ) is characterised by distinct ice floes and its direct exposure to the open ocean. Sea ice is typically described as a continuous material but this description can be inappropriate in an MIZ due to the granular nature of the ice cover and the scale of processes acting on the ice floes. In this thesis, the kinematic behaviour of sea ice in an MIZ modelled as a granular material is investigated with an emphasis on the influence of ocean waves. The kinematic behaviour of a set of ice floes subject to ocean wave forcing was recorded in an experiment conducted in the Ross Sea. Kinematic data were recorded from each ice floe using a GPS receiver, tri-axial accelerometer, and compass. The data show (1) the influence of wave forcing and (2) collisions between neighbouring ice floes. It was also discovered that the GPS receivers were able to resolve the effects of ocean wave forcing despite their poor absolute accuracy. The number density and normalised structure factor (NSF) are introduced to describe the spatial structure of a set of ice floes. Four idealised distributions (in 1D and 2D) are analysed to gain insight into the way that different factors determine the shape of the NSF. It is shown that (1) a significant sinusoidal deviation causes a peak in the NSF, (2) ordered structure dominates low spatial frequencies, and (3) disorder dominates high spatial frequencies. A comparison of the contributions from these different factors is used to estimate the significance of a sinusoidal deviation in the positions of the ice floes. A granular model of an MIZ is developed using a novel set of equations of motion to examine the effect of ocean wave forcing. The equations of motion are derived for small ice floes and allows forcing by multiple waves. These equations predict a transient, wave-induced torque, which can be sustained by the application of a second force to the ice floe. Torque induced by the interaction of two forces on an ice floe may be a general feature of sea ice motion. The number density and NSF are used to analyse the distribution of ice floes in the granular model. At low solids-fractions the number density is correlated at the frequency of the wave forcing. As the solids-fraction is increased this correlation is destroyed by collisions between the ice floes and new correlations are created that are related to the packing structure of the ice floes. When the number density is weighted by the velocity of the ice floes, the correlations between floes are related to the convolution of the wave velocity field and the number density. These correlations may be incorporated into the thickness distribution of large-scale models using the maximum entropy method. The granular model was also examined as a percolating network of contacts and it was found that percolation was more likely to occur along the crest of a wave than in the direction of propagation.

The West Antarctic Ice Sheet (WAIS) is currently thinning and retreating because shifting oceanic currents are transporting warmer waters to the ice margin, which could lead to a collapse of the ice sheet and global sea level rise. International Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in 2018 to study the history of the WAIS over the last 20 million years. Previous geologic drilling projects into Ross Sea sediments that record the history of the WAIS (DSDP Leg 28, RISP, MSSTS, Cape Roberts Drilling Project, ANDRILL), as well as modeling studies, show considerable variability of ice-sheet extent during the Neogene and Quaternary including ice sheet collapse during times of extreme warmth. The purpose of this study is to reconstruct paleoenvironments on the Ross Sea and confirm modeling studies that show warming waters in the Southern Ocean led to the loss of Antarctic ice in the past. Site U1523 is a key site as it is located close to the shelf break and therefore sensitive to warm water incursions from modified Circumpolar Deep Water (mCDW) onto the Ross Sea continental shelf as the Antarctic Slope Current weakens with a changing climate. Shelf sites U1522 and U1521 provide perspective for what was happening closer to the Ross Ice Shelf. Multiple incursions of subpolar or temperate planktic foraminifera taxa occurred during the latest Pliocene and early Pleistocene prior to ~1.8 Ma at Site U1523 indicating times of warmer than present conditions and less ice in the Ross Sea. Especially high abundances of foraminifera are recorded in the late Pleistocene associated with Marine Isotope Stage (MIS) 31, MIS 11, and MIS 5e might also indicate reduced ice and relatively warmer conditions. The interval of abundant foraminifera around MIS 31 (MIS 37 to 21) suggests multiple warmer interglacials during the Mid-Pleistocene Transition (MPT). A change in benthic foraminiferal assemblages and a large increase in foraminiferal fragments after the MPT (~800 ka) indicate stronger currents at the seafloor and perhaps corrosive waters, suggesting a major change in water masses entering (mCDW) or exiting the Ross Sea (AABW) since the MPT.

Indiana University-Purdue University Indianapolis (IUPUI) / Petrography of the sand fraction, particle size analysis, and detrital zircon U/Pb isotope data, and pebble count data were collected from Byrd Glacier moraines and central/western Ross Sea till in order to study the glacially-driven sedimentological dynamics of the Byrd Glacier and to trace material transported from the Byrd Glacier into the Ross embayment. Most of the petrographic data show evidence of local derivation with the exception of the sites from the Lonewolf Nunataks as indicated by exotic rock types within the sand and pebble fractions. This, in conjunction with particle-size data of the samples from the Lonewolf Nunataks indicate that material from underneath the East Antarctic Ice Sheet (EAIS) is being transported to the surface and deposited in this area. The U/Pb ages of zircons from the Byrd Glacier show dominant populations of Ross to Pan-African ages (~533 - 610 Ma) with varying populations of older (Grenville to Archean) zircons. Late Precambrian (~588 – 610 Ma) aged detrital zircons in samples from the head of the Byrd Glacier are older than other dated grains found in the vicinity and may be evidence of early development of the Ross belt or represent evidence of sub-glacial extension of the Mozambique structure found in Dronning Maud Land. The west central Ross Sea till samples have a variety of mineral and lithic fragments that include a dominant population of polymict at certain depth intervals. Detrital zircon data suggests the potential provenance of two of these intervals may be derived from Marie Byrd Land and possibly the Byrd Glacier. Using sand petrography and U/Pb detrital zircon age dating, positive correlation was found between specific samples from the head of the Byrd Glacier and the western Ross Sea. The ice-sheet flow models of Stuiver et al. (1981), Licht and Fastook (1998), and Licht et al. (2005) each show potential support from aspects of this study. It is possible that dynamic ice-flow regime changes of the West and East Antarctic Ice Sheets into the Ross Sea may have occurred some time during the LGM as suggested by geochemical and petrographical evidence found within intervals of central and western Ross Sea cores.

Basal melting of ice shelves is causing accelerating mass loss from the Antarctic Ice Sheet, yet the oceanographic processes which drive this are rarely observed. This thesis uses new observations from phase sensitive radar and moored oceanographic instruments to describe the processes which drive rapid basal melting of the north-western Ross Ice Shelf. Oceanographic conditions at the mooring site are strongly influenced by the neighbouring Ross Sea Polynya. High Salinity Shelf Water fills the lower water column continuously, but during summer a southward flow ventilates the cavity bringing Antarctic Surface Water (AASW) to the site. Tides account for half of the flow speed variance, and low frequency variability is influenced by local winds, and eddies associated with sea ice production in the polynya. Four years of basal melt rate observations show a mean melt rate of 1.8 m y$^{-1}$ at the mooring site and a strong seasonal cycle driven principally by water temperature variations. Radar observations show that melt rates vary rapidly and continuously in response to flow speed variability, and rapid melting occurs only when flow speeds are high. Radar observations of melt rates from 78 sites on the Ross and McMurdo ice shelves show an area-averaged annual-mean basal melt rate of 1.35 m y$^{-1}$, implying a net basal mass loss of 9.6 Gt y$^{-1}$ from the region. Melt rates are highest near the ice front where annual-mean and short-term summer rates reached 7.7 m y$^{-1}$ and 53 m y$^{-1}$, respectively. The seasonal and spatial variations in melt rate are consistent with melting driven by the summer inflow of AASW. Observations of boundary layer water temperature, flow speed and melt rates indicate that melt rates scale linearly with current speed, but sub-linearly with temperature in the outer boundary layer, possibly due to the stabilising effects of melt water input. Existing melt rate parameterisations which account for flow speed can be tuned to match the observations when thermal driving is low, but overestimate melt rates at higher temperatures, implying the need for further refinements to the models.

No description available.