Dissolution index and shell weights of planktonic foraminifera

Finding the ideal deep-sea CaCO3 dissolution proxy is essential for quantifying the role of the marine carbonate system in regulating atmospheric pCO2 over millennia. We explore the potential of using the Globorotalia menardii fragmentation index (MFI) and size-normalized foraminifer shell weight (SNSW) as complementary indicators of deep-sea CaCO3 dissolution. MFI has strong correlations with bottom water [CO3]2-, modeled estimates of percent CaCO3 dissolved, and Mg/Ca in Pulleniatina obliquiloculata in core top samples along a depth transect on the Ontong Java Plateau (OJP) where surface ocean temperature variation is minimal. SNSW of P. obliquiloculata and Neogloboquadrina dutertrei have weak correlations with MFI-based percent dissolved, Mg/Ca in P. obliquiloculata shells and bottom water [CO3]2- on the OJP. In core top samples from the eastern equatorial Pacific (EEP), SNSW of P. obliquiloculata has moderate to strong correlations with both MFI-based percent CaCO3 dissolved estimates and surface ocean environmental parameters. SNSW of N. dutertrei shells shows a latitudinal distribution in the EEP and a moderately strong correlation with MFI-based percent dissolved estimates when samples from the equatorial part of the region are excluded. Our results suggest that there may potentially be multiple genotypes of N. dutertrei in the EEP which may be reflected in their shell weight. MFI-based percent CaCO3 dissolved estimates have no quantifiable relationship with any surface ocean environmental parameter in the EEP. Thus MFI acts as a reliable quantitative CaCO3 dissolution proxy insensitive to environmental biases within calcification waters of foraminifers.

Ice-rafted debris in ODP Holes 177-1090D and 188-1165B

Constraining the nature of Antarctic Ice Sheet (AIS) response to major past climate changes may provide a window onto future ice response and rates of sea level rise. One approach to tracking AIS dynamics, and differentiating whole system versus potentially heterogeneous ice sheet sector changes, is to integrate multiple climate proxies for a specific time slice across widely distributed locations. This study presents new iceberg-rafted debris (IRD) data across the interval that includes Marine Isotope Stage 31 (MIS 31: 1.081-1.062 Ma, a span of ~19 kyr; Lisiecki and Raymo, 2005), which lies on the cusp of the mid-Brunhes climate transition (as glacial cycles shifted from ~41,000 yr to ~100,000 yr duration). Two sites are studied - distal Ocean Drilling Program (ODP) Leg 177 Site 1090 (Site 1090) in the eastern subantarctic sector of the South Atlantic Ocean, and proximal ODP Leg 188 Site 1165 (Site 1165), near Prydz Bay, in the Indian Ocean sector of the Antarctic margin. At each of these sites, MIS 31 is marked by the presence of the Jaramillo Subchron (0.988-1.072 Ma; Lourens et al., 2004) which provides a time-marker to correlate these two sites with relative precision. At both sites, records of multiple climate proxies are available to aid in interpretation. The presence of IRD in sediments from our study areas, which include garnets indicating a likely East Antarctic Ice Sheet (EAIS) origin, supports the conclusion that although the EAIS apparently withdrew significantly over MIS 31 in the Prydz Bay region and other sectors, some sectors of the EAIS must still have maintained marine margins capable of launching icebergs even through the warmest intervals. Thus, the EAIS did not respond in complete synchrony even to major climate changes such as MIS 31. Further, the record at Site 1090 (supported by records from other subantarctic locations) indicates that the glacial MIS 32 should be reduced to no more than a stadial, and the warm interval of Antarctic ice retreat that includes MIS 31 should be expanded to MIS 33-31. This revised warm interval lasted about 52 kyr, in line with several other interglacials in the benthic d18O records stack of Lisiecki and Raymo (2005), including the super-interglacials MIS 11 (duration of 50 kyr) and MIS 5 (duration of 59 kyr). The record from Antarctica-proximal Site 1165, when interpreted in accord with the record from ANDRILL-1B, indicates that in these southern high latitude sectors, ice sheet retreat and the effects of warming lasted longer than at Site 1090, perhaps until MIS 27. In the current interpretations of the age models of the proximal sites, ice sheet retreat began relatively slowly, and was not really evident until the start of MIS 31. In another somewhat more speculative interpretation, ice sheet retreat began noticeably with MIS 33, and accelerated during MIS 31. Ice sheet inertia (the lag-times in the large-scale responses of major ice sheets to a forcing) likely plays an important part in the timing and scale of these events in vulnerable sectors of the AIS.

Ichthyoplankton density and zooplankton biomass in the northern Benguela upwelling system during D356 September 2010

Ichthyoplankton density (fish eggs and larvae) and bulk zooplankton biomass in September 2010 were determined for 10 stations in the northern Benguela upwelling system, based on oblique Multinet hauls during the RRS Discovery D356 cruise. A HYDROBIOS Multinet, type Midi (0.25 m**2 mouth area) was equipped with five nets of 500 µm-mesh size, temperature and oxygen probes, and an inner and outer flow meter to monitor the net's trajectory (for volume filtered calculations) as well as net clogging. The Multinet was handled over the side, towed horizontally at 2 knots. Winch speed when fearing was 0.5 or 0.3 m/s, heaving velocity 0.2 - 0.3 m/s. The Multinet was towed obliquely at 10 stations sampling the upper 200 m of the water column, which were divided into five different depth strata after inspection of temperature and oxygen concentration depth profiles. Ichthyoplankton densities and zooplankton biomass were calculated for each depth stratum (=single net) from total abundance and the volume of water filtered [individuals per m**3 and g wet weight per m**3, respectively]. In addition, densities and biomass were integrated over the area for each station [individuals per m**2], as sum of calculations for each net: Sum ([individuals per m**3]*Delta(depth bot[m]-depth top [m]).

Ichthyoplankton density and zooplankton biomass in the Benguela upwelling system during AFR258 in December 2009

IIchthyoplankton density (fish eggs and larvae) and bulk zooplankton biomass in December 2009 were determined for 22 stations in the Benguela upwelling system, based on oblique Multinet hauls during the FRS Africana cruise AFR258. A HYDROBIOS Multinet, type Midi (0.25 m**2 mouth area) was equipped with five nets of 500 µm-mesh size, temperature and oxygen probes, and an inner and outer flow meter to monitor the net's trajectory (for volume filtered calculations) as well as net clogging. The Multinet was handled over the side, towed horizontally at 2 knots. Winch speed when fearing was 0.5 or 0.3 m/s, heaving velocity 0.2 - 0.3 m/s. The Multinet was towed obliquely at 22 stations sampling the upper 200 m of the water column, which were divided into five different depth strata after inspection of temperature and oxygen concentration depth profiles. Ichthyoplankton densities and zooplankton biomass were calculated for each depth stratum (=single net) from total abundance and the volume of water filtered [individuals per m**3 and g wet weight per m**3, respectively]. Densities and biomass were integrated over the area for each station [individuals per m**2], as sum of calculations for each net: Sum ([individuals per m**3]*Delta (depth bot[m]-depth top [m]).