5.3.1 Eastern Campbell Plateau:
Trends in Holocene bathymetry of deep-water masses
Care S0136-019BX
The slightly decreasing influence of factor 1, which resembles the "Nuttalides umbonifer association" indicates sinking of the AABW. Depletion of the planktic Öl80 isotope ratio from 18.5 cm bsf upwards is accompanied by slightly increasing loading of factor 2, which indicates increasing influence of CPDW. A sudden change from AABW to CPDW is located at 13.5 cm bsf. Considering rising surface temperatures and sinking of the upper border of the AABW, the Subpolar Front might have moved southward. The faunal associations of the upper 4.5 cm of the core are overprinted by dominance of agglutinating species. Therefore, the faunal associations are not conclusive. Early diagenetic processes cause the pattern of abundance of agglutinating species. This might indicate an undisturbed stratification of the upper part of the core. This assumption is supported by the observation, that the change of the water masses is located in the same sediment depth as in care S0136-037BX. However, these hints are not conclusive due to the lack of an age model. The variations in the planktic and especially in the benthic stable isotope ratio hints strong redeposition and probably sedimentation of down slope material.
Core S0136-037BX
The observed trend of sinking water masses recognised in core S0136-019BX is supported by results found in this care: The loadings of factors 2 and 3 increase in the lower sections of the core and indicate infIuence of the CPDWu. The rising infIuence of factor 1, which indicates the Antarctic Intermediate Water (AAIW) is accompanied by a short phase of increased carbonate dissolution. It is to mention that the beginning of the infIuence of the present water mass is located at the same depth as in core S0136-019BX. The correlation of the trend of planktic Öl80 isotope ratios with the ratios of the cores from the South Tasman Rise revealed an age of about .... 12000 yr. for this core. Following this model, the change from CPDWu to AAIW should be located at the end of the ACR (see Figure 5.3. p. 71). However, as far as no absolute ages are available, this age model is not conc1usive. Effects of early diagenesis on the foraminifera fauna are present and serve as evidence for arecent surface. As far as the composition of benthic faraminifera faunal varies only slightly in the upper 12.5 cm of the core, the faunal association of factor 1 should indicate the water mass the care is recently bathed in. It is to mention that no signs for redeposition are present in this core.
5.3.2 South Tasman Rise:
Trends in bathymetry of deep-water masses and ecological responses of benthic foraminiferal assemblages.
The faunal associations of the upper sections of all cores indicate rising infIuence of the water mass below. This is interpreted as a generally rising trend of the water masses, which might be accompanied with enhanced mixing of the water masses.
Core S0136-147BX
The care shows minor variations in paleoceanography. The observed patterns in benthic foraminifera fauna represent the normal variabilities of an ecosystem, which might be overprinted by bioturbation or erosional and redepositional processes. The benthic foraminiferal association mirrors the low oxygen conditions of the CPDWu. The short infIuences of species that indicate oxic conditions might indicate increased ventilation of the sediment due to strong currents.
Core S0136-161BX
The abundances of benthic foraminifera might mirror two trends:
A general shallowing of the water mass body is indicated by increasing influence of the epifaunal "Epistominella exigua association" to the top of the core, and accompanied by increasing
a
l80 isotope ratio of C. wuellerstorfi.The climate variations, which are indicated by the planktic
a
l80 record can be traced in the infaunal benthic foraminiferal fauna. M. pompilioides shows higher abundances in phases of decreased surface temperatures. U. peregrina is prevailing in the Holocene climate optimum, though it does not show as clear correlations as M. pompilioides to colder temperatures. The ecological preferences of the described species differ only scarcely. All species prefer an infaunal lifestyle and indicate high nutrient fluxes and low oxygen conditions in the sediment. The variations in the faunal associations are probably due to slight changes in quantity (and quality ?) of food supply. These variations seem to be caused by changes in surface temperature and followed variation of primary production.Core S0136-165BX
The core shows overprinting of three signals:
The most dominant feature is a high productivity event in the lower two sections of the core, indicated by high abundance of F. contemplata. Movement of the Subtropical Front might have caused this high productivity event over the core position. The abundance of F.
contemplata anti-correlates with sea surface temperature as indicated by
a
l80 ratio.A second feature is the variation of sea surface temperature that can be traced in the benthic fauna, as described for core S0136-161BX.
A general shallowing trend of the water mass body is indicated by increasing influence of N.
umbonifer to the top of the core. The increasing influence of the carbonate aggressive AABW is supported by the counting of fragments of foraminifera tests in core S0136-164GC. The amount of fragments increases towards the upper centimeter of the core (personal com. A. Sturm, GEOMAR).