WEAK PLIOCENE BOTTOM CURRENTS IN THE JANE BASIN, NW WEDDELL SEA BASED ON MULTIVARIATE ANALYSIS OF GRAIN SIZE SPECTRA

Abstract. The Weddell Sea and the associated Filchner-Rønne Ice Shelf constitute key regions for global bottom-water production today. However, little is known about bottom-water production under different climate and ice-sheet conditions. Therefore, we studied core PS1795, which consists primarily of fine-grained siliciclastic varves that were deposited on contourite ridges in the southeastern Weddell Sea during the Last Glacial Maximum (LGM). We conducted high-resolution X-ray fluorescence (XRF) analysis and grain-size measurements with the RADIUS tool (Seelos and Sirocko, 2005) using thin sections to characterize the two seasonal components of the varves at sub-mm resolution to distinguish the seasonal components of the varves. Bright layers contain coarser grains that can mainly be identified as quartz in the medium to coarse silt grain size. They also contain higher amounts of Si, Zr, Ca, and Sr, as well as more ice-rafted debris (IRD). Dark layers, on the other hand, contain finer particles such as mica and clay minerals from the chlorite and illite groups. In addition, chemical elements, Fe, Ti, Rb, and K are elevated as well. Based on these findings as well as on previous analyses on neighbouring cores, we propose a model of glacially enhanced thermohaline convection in front of a grounded ice sheet that is supported by seasonally variable coastal polynya activity. Accordingly, katabatic (i.e. offshore blowing) winds removed sea ice from the ice edge, leading to coastal polynya formation. We suggest that glacial processes were similar to today with stronger katabatic winds and enhanced coastal polynya activity during the winter season. If this is correct, silty layers are likely glacial winter deposits, when brine rejection was increased, leading to enhanced bottom water formation and increased sediment transport. Vice versa, finer-grained clayey layers were then deposited during summer, when coastal polynya activity was likely reduced.

Download Full-text

Statistical Relationship Between Multibeam Backscatter, Sediment Grain Size and Bottom Currents

Proceedings of the 10th National Technical Seminar on Underwater System Technology 2018 - Lecture Notes in Electrical Engineering ◽

10.1007/978-981-13-3708-6_11 ◽

2019 ◽

pp. 121-133

Author(s):

Mohd Azhafiz Abdullah ◽

Razak Zakariya ◽

Rozaimi Che Hasan

Keyword(s):

Grain Size ◽

Statistical Relationship ◽

Sediment Grain Size ◽

Bottom Currents

Download Full-text

Iceland-Faroe Ridge overflow dynamics, 55-6 ka BP

10.5194/egusphere-egu2020-11245 ◽

2020 ◽

Author(s):

Maryam Mirzaloo ◽

Dirk Nürnberg ◽

Markus Kienast ◽

Jeroen van der Lubbe

Keyword(s):

Grain Size ◽

Ocean Circulation ◽

Academic Career ◽

Meridional Overturning Circulation ◽

Bottom Current ◽

Oceanic Circulation ◽

Climate Conditions ◽

Bottom Currents ◽

The Past ◽

Bulk Chemistry

The understanding of the past changes in this critical area of oceanic circulation will be beneficial to predict future climate conditions and their related socio-economic impacts. Sediment cores recovered from the western flank of the Iceland-Faroe Ridge (IFR; P457-905 and -909) provide unique archives to reconstruct changes in the Iceland-Scotland overflow water (ISOW), an important component of the Atlantic Meridional Overturning Circulation (AMOC) over the last 55-6 ka BP. We provide high-resolution records of lithogenic grain-size and XRF bulk chemistry on millennial timescales. The age models of both cores have been constrained by radiocarbon datings of planktonic foraminifera and distinct tephra layers, which include the well-known Faroe-Marine-Ash-Zones (FMAZ) II and III. Both grain-size and XRF bulk chemistry (Zr/Rb and Ti/K) reveal prominent Dansgaard-Oeschger sedimentary cycles, which reflect considerable changes in near-bottom current strength and sediment transport/deposition. The transition between cold Greenland Stadials (GSs) and warm Greenland Interstadials (GIs) occur in typical, recurring sedimentation patterns. The GIs are characterized by relatively strong bottom currents and the transport/deposition of basaltic (Ti-rich) silts from local volcanic sources resembling the modern ocean circulation pattern. In contrast, fine grained felsic (K-rich) sediments were deposited during GSs, when the ISOW was weak. In particular, the Heinrich (like) Stadials HS1 and HS2 stand out as intervals of very fine felsic sediment deposition and hence, slackened bottom currents. The bottom currents appear to progressively strengthen throughout the GIs, and sharply decline towards the GSs. This pattern contrasts with records from north of the IFR, which might be explained by a diminishing contribution of the flow cascading over the IFR. Together, these new records show strong changes in bottom current dynamics related to the Iceland-Scotland overflow, which has a strong influence on the past and modern climate of the North Atlantic Region. However, climate change is an interdisciplinary field of research. HOSST-TOSST transatlantic interdisciplinary research program provides the unique opportunity for constructive communication and collaboration among scientists with different skills filling knowledge gaps and bridging the earth sciences with social and economic disciplines. Such interdisciplinary programs at early stages in an academic career is necessary to move and encourage the new generation of the scientific community toward a tradition of broad&#8208;scale interactions.&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;

Download Full-text

A Grain Size Spectra Map

Journal of Sedimentary Research ◽

10.1306/212f7153-2b24-11d7-8648000102c1865d ◽

1977 ◽

Vol Vol. 47 ◽

Author(s):

John J. Dowling

Keyword(s):

Grain Size ◽

Size Spectra

Download Full-text

Modelling of single-grain and floc settling

Canadian Journal of Earth Sciences ◽

10.1139/e89-215 ◽

1989 ◽

Vol 26 (12) ◽

pp. 2523-2528

Author(s):

Y. L. Lau

Keyword(s):

Grain Size ◽

Analytical Model ◽

Total Concentration ◽

Finite Depth ◽

Time Dependent ◽

Size Spectra ◽

Fine Sediments ◽

Single Grain ◽

Modal Size

An analytical model of time-dependent settling in a suspension of finite depth is presented. The model correctly predicts the decrease in total concentration of three suspensions of fine sediments undergoing single-grain settling. The changes in grain-size spectra, in which decrease in concentration occurs mainly in sizes larger than the modal size, are also predicted. The model is used with data from the settling of flocculated suspensions to show that the rate of flocculation is approximately proportional to the second power of the concentration.

Download Full-text