Soluble salt accumulations in Taylor Valley, Antarctica: Implications for paleolakes and Ross Sea Ice Sheet dynamics

<p>The Ross Ice Shelf is the Antarctic region that over the last deglaciation experienced the greatest change in areal ice cover. Today, cold, dense and saline water masses (brines) produced in the Ross Sea polynya, flow from the shelf to the deep ocean providing a significant contribution to the propelling of the global ocean circulation regulating the climate. In particular, the Hillary Canyon in the Eastern Ross Sea is the main conduit through which brines descend the slope to reach the deeper ocean and is thus one of the greatest regions of cold, dense water export in the world.</p><p>A Contourite Depositional System (the ODYSSEA CDS) on the western flank of the Hillary Canyon is inferred to have been generated through several hundred-thousand years by along-slope, contour currents that transported and accumulated the sediments brought down the Hillary Canyon by means of brines. A multi-proxy investigation was conducted on the shallowest part of the ODYSSEA CDS depositional sequences, which we expect to contain i) the record of the brine formation, ii) the indication on contour current strength through time, and iii) their interplay and modulation associated to climate change.</p><p>Six gravity cores, collected in both the proximal and distal area of the ODYSSEA CDS, were studied through multi-proxy analyses including sediment physical properties (texture, structures, water content, wet bulk density), compositional characteristics (XRF, geochemistry and detrital apatite, zircon, and rutile U-Pb on ice-rafted debris) (Lucchi et al., 2019; Neofitu et al., 2020) and microfossil content (planktonic and benthic foraminifera, calcareous nannofossils and diatoms). An age model has been reconstructed combining palaeomagnetic record, biostratigraphic content, tephrochronology and AMS radiocarbon dating on planktonic foraminifera tests.</p><p>Inferred variations in dense water formation, contour current strength and <strong>ice sheet dynamics </strong>are discussed in the light of our data interpretation.</p><p>&#160;</p><p>Lucchi, R.G., Caburlotto, A., Miserocchi, S., Liu, Y., Morigi, C., Persico, D., Villa, G., Langone, L., Colizza, E., Macr&#236;, P., Sagnotti, L., Conte, R., Rebesco, M., 2019. The depositional record of the Odyssea drift (Ross Sea, Antarctica). Geophysical Research Abstracts, Vol. 21, EGU2019-10409-1, 2019. EGU General Assembly, Vienna (Austria), 7&#8211;12, April, 2019 (POSTER).</p><p>Neofitu, R., Mark, C., Rebesco, M., Lucchi, R.G., Douss, N., Morigi, C., Kelley, S., Daly, J.S., 2020. Tracking Late Quaternary ice sheet dynamics by multi-proxy detrital mineral U-Pb analysis: A case study from the Odyssea contourite, Ross Sea, Antarctica. Geophysical Research Abstracts. EGU General Assembly, Vienna (Austria), 3&#8211;8, May, 2020 (POSTER for session CL1.11).</p>

Download Full-text

Pleistocene cyclostratigraphy on the continental rise and abyssal plain of the western Ross Sea, Antarctica

10.26686/wgtn.17061797 ◽

2021 ◽

Author(s):

◽

Olga Al'bot

Keyword(s):

Sea Ice ◽

Ross Sea ◽

Ice Sheet ◽

Abyssal Plain ◽

Early Pleistocene ◽

Sand Fraction ◽

X Ray ◽

Continental Rise ◽

Western Ross Sea

<p>This thesis investigates glacimarine sedimentation processes operating on the continental margin of the western Ross Sea during the Pleistocene (˜2.5 Ma). This time period is characterised by a major global cooling step at ˜0.8 Ma, although several proposed episodes of major marine-based Antarctic Ice Sheet (AIS) retreat in warm interglacial periods are inferred to have occurred after this time. Constraining the timing and magnitude of past marine-based AIS retreat events in the Ross Sea through this time will improve our understanding of the forcing mechanisms and thresholds that drive marine-based ice sheet retreat. Identifying such mechanisms and thresholds is crucial for assisting predictive models of potential ice sheet collapse in a future world with rapidly rising atmospheric carbon dioxide (CO₂) concentrations. Six sedimentary cores forming a north-to-south transect from the continental rise to the abyssal plain of the western Ross Sea were examined in order to identify potential sedimentary signatures of past marine-based ice sheet variability and associated oceanographic change. A lithofacies scheme and stratigraphic framework were developed, which allowed the identification of shifting sedimentary processes through time. The sediments are interpreted to have been deposited primarily under the influence of bottom currents, most likely from changing rates of dense Antarctic Bottom Water (AABW) formation over glacial-interglacial cycles. Two dominant lithofacies (laminated and bioturbated) are recognised in the Pleistocene contourite sequences. Laminated facies alongside reduced ice-rafted debris (IRD) fluxes and reduced biological productivity are interpreted to represent expanded ice sheet and sea ice margins during glacial conditions, which acted to restrict surface water ventilation resulting in less oxygenated bottom waters. Conversely, laminated facies alongside reduced IRD fluxes and increased productivity are inferred to represent a reduction of ice shelf and sea ice cover resulting in enhanced AABW formation and sediment delivery. In general, it is interpreted that bioturbated facies in combination with enhanced productivity are common during interglacial conditions, with peaks in IRD associated with ice sheet retreat events leading into interglacial conditions. However, the relationships between laminated and bioturbated facies vary between sites, and facies at most sites generally alternate on timescales exceeding that of individual glacial-interglacial cycles (<100 kyr). Nonetheless, there are clear baseline shifts in the facies distributions through time across the sites, and it is inferred these represent step-like shifts in the ice sheet volume and sea ice processes on the continental shelf and above the study sites during the Pleistocene. This thesis also assesses and compares three independent methodologies of obtaining IRD mass accumulation rates (MARs). The three methodologies include counting clasts >2 mm in x-ray images, the sieved weight percentage of the medium-to-coarse sand fraction (250 µm-2 mm), and volumetric estimates of the > 125 µm sand fraction using a laser particle sizer. The x-ray and sieve methods produced comparable results, while the volumetric estimate, although showing comparable long-term trends, produces a lesser correlation to the other two methods. Spectral analysis of the IRD content and the magnetic susceptibility data series reveals that during the Early Pleistocene (2.5-1.2 Ma) ice discharge into the western Ross Sea was paced by the 41 kyr and 100 kyr cycles of obliquity and eccentricity, respectively. The Mid-Pleistocene Transition (MPT;1.2-0.8 Ma) was characterised by a switch to a higher-frequency, lower-amplitude IRD flux during a long-term period of high power in eccentricity, obliquity and precession (˜23 kyr) observed in the orbital solutions, suggesting a relatively linear response to orbital forcing at this time. The colder climate state of the Late Pleistocene (0.8-0.01 Ma) is characterised by IRD fluctuations modulated primarily by the 100 kyr eccentricity forcing that became dominant by 400 ka. In the western Ross Sea, IRD fluxes show a clear response to the orbital pacing of glacial-interglacial cycles, but are equivocal in identifying the magnitude of ice sheet loss or growth through glacial-interglacial cycles.</p>

Download Full-text

Recent recovery of Antarctic Bottom Water formation in the Ross Sea driven by climate anomalies

10.5194/egusphere-egu21-8371 ◽

2021 ◽

Author(s):

Alessandro Silvano ◽

Annie Foppert ◽

Steve Rintoul ◽

Paul Holland ◽

Takeshi Tamura ◽

...

Keyword(s):

Sea Ice ◽

Continental Shelf ◽

Bottom Water ◽

Ross Sea ◽

Ice Sheet ◽

Ice Formation ◽

Depth Range ◽

Antarctic Bottom Water ◽

Climate Anomalies ◽

The Antarctic

<div> <div> <div> <p>Antarctic Bottom Water (AABW) supplies the lower limb of the global overturning circulation, ventilates the abyssal ocean and sequesters heat and carbon on multidecadal to millennial timescales. AABW originates on the Antarctic continental shelf, where strong winter cooling and brine released during sea ice formation produce Dense Shelf Water, which sinks to the deep ocean. The salinity, density and volume of AABW have decreased over the last 50 years, with the most marked changes observed in the Ross Sea. These changes have been attributed to increased melting of the Antarctic Ice Sheet. Here we use in situ observations to document a recovery in the salinity, density and thickness (that is, depth range) of AABW formed in the Ross Sea, with properties in 2018&#8211;2019 similar to those observed in the 1990s. The recovery was caused by increased sea ice formation on the continental shelf. Increased sea ice formation was triggered by anomalous wind forcing associated with the unusual combination of positive Southern Annular Mode and extreme El Ni&#241;o conditions between 2015 and 2018. Our study highlights the sensitivity of AABW formation to remote forcing and shows that climate anomalies can drive episodic increases in local sea ice formation that counter the tendency for increased ice-sheet melt to reduce AABW formation.</p> </div> </div> </div>

Download Full-text