Del objetivo específico N° 1

Polar Star Cruises, Summer 1992 and 1993

{Core PS2177-5 (KAL), Core PS2200-5, Core PS2212-3 and Core PS2185-6.} {Core PI-92-AR 39, Core PI-92-AR 30, Core PI-92-AR 27 and Core PI-93-AR 2 1.}

1. Cores were collected from the Lomonosov Ridge, Morris Jesup Rise and Yermak Plateau in the eastern Arctic Basin, namely the Eurasian Basin. A total of 273 sediment samples were examined from the cores with 27 (Core PS2177-5), 26 (PS2185-6), 80 (PS2200-5), and 9 samples (PS2212-3) yielding DWAF respectively.

2. All of the Polar Star cores were collected from the Northwind Ridge, in the Canada Basin in the western part (Amerasian Basin) of the Arctic Ocean. DWAF were recovered from 290 out of a total of 706 sediment samples. Agglutinated foraminifera were present in: 84 samples (Core PI-92-AR 39); 75 samples (92-30); 57 samples (92-27); and 74 samples (93-21).

3. Fifteen species are present in the four Eurasian Basin and Amerasian Basin cores. The main species include Cyclammina pusilla, A lveolophragm ium polarensis, Trochammina lomonosovensis, Psammosphaera fusca, Rhabdammina discreta, Glomospira charoides, G. gordialis and Cystammina pauciloculata (see Appendix I). Species that are unique to the Polarstern cores are Glomospira saturniformis and one specimen of Reophax sp. A specimen of Textularia in the Canada Basin was the only different species in comparison with the German cores.

4. Cyclammina pusilla dominates all the cores from both basins, except Core PS2212-3, which is dominated by Alveolophragmium polarensis. The latter is present in all the cores, except in Core PS2177-5. In three cores from the Canada Basin, the smaller fractions are dominated by Glomospira charoides (92-39, 92-30, 92-27). The smaller fraction of 93-21 is dominated by Cystammina pauciloculata.

8.2 Chronostratigraphy of Core PS2177-5 (KAL), Core PS2200-5, Core PS2212-3 and Core PS2185-6.

1. This study uses chronostratigraphic models determined by previous workers for the Eurasian Basin cores (see Chapter 5). Stratigraphie ranges of DWAF from this study were plotted against the models, with the exception of Core PS2177-5 where no age model was available. ^^C -AMS dates were determined by previous workers

in one of the Eurasian Basin cores, Core PS2185-6. Two age models were determined for some of the Eurasian Basin cores using palaeomagnetic analyses (for discussion see Chapters 5, 7, Frederichs 1995).

2. Many of the ranges are plotted for the first time from the Pliocene-Pleistocene of the central Arctic Ocean. Core PS2185-6 is the oldest core studied from the Eurasian Basin, ranging from the Gilbert Chron at its base through to the top of the Brunhes Chron (see Figure 7.2.2.1). Cyclammina pusilla is present from the base of this core, to the base of the Brunhes chronozone (mid oxygen isotope Stage 14) and reappears in oxygen Stage 13, with a LAD in oxygen isotope Stage 10. Other DWAF in Core PS2185-6 occur more sporadically, with A. polarensis and G.

gordialis ranging from the base of the core until oxygen isotope Stages 7 and 10 respectively (mid-Brunhes Chron). Trochammina lomonosovensis is the youngest occurring species in Core PS2185-6, and has its LG in oxygen isotope Stage 4. The remaining species in Core PS2185-6 are restricted to the Gilbert and Gauss chronozones.

3. DWAF species in Core PS2200-5 occur from its base, ranging from oxygen isotope Stage 14 to Stage 1. (see Figure 7.2.2.1). The dominant species, C. pusilla

occurs from oxygen isotope Stage 14 until Stage 7, and is last recorded in oxygen isotope Stage 5. Alveolophragmium polarensis has the longest range occurring from oxygen isotope Stage 14 to Stage 11, with subsequent abundance peaks in oxygen isotope Stages 9, 8, 7, 5 and is last recorded in Stage 1. DWAF species in Core PS2212-3 have the shortest ranges of all the Eurasian Basin cores as it is the youngest of all four cores. Alveolophragmium polarensis, which dominates the assemblage ranges from oxygen isotope Stage 3 to Stage 1. This is a slightly longer range compared with P. fusca which is present in oxygen isotope Stages 2 and 1. All of the other species in the core are restricted to oxygen isotope Stage 5.

8.3 Chronostratigraphy of Core PI-92-AR 39, Core PI-92-AR 30, Core PI-92-AR 27 and Core PI-93-AR 21.

1. Age models for the Canada Basin cores were determined by U.S.G.S. scientists (Poore et al. in prep.). The age models are include two key lithostratigraphic units, the egelida bed (represented by the planktonic foraminifera, Globigerina egelida),

the mud clast unit (MCU) and the presence of the "Brown Beds". Palaeomagnetic analyses indicated that the cores ranged in age from the Gilbert Chron in the lower section of Core PI-93-AR 21 to the Brunhes Chron in all cores.

2. Core PI-93-AR 21 from the Northwind Ridge, represents the longest age range, from the Gilbert (base of core 5.7 Ma) through to the Brunhes Chron. The dominant species, C. pusilla is present from the Gilbert chronozone (Unit A) occurring with small stratigraphie hiatuses until the upper Matuyama (Unit J, see Figure 7.2.2.2). This stratigraphie range is comparable to that of T. lomonosovensis. Alveolophragmium polarensis and Cystammina pauciloculata'

ra n ^ are shorter, from the core base (Gilbert chronozone. Unit A), to the base of A the Matuyama (Unit B). Psammospheara fusca is present in the uppermost Brunhes

chronozone. This represents the shortest stratigraphie range and youngest occurring species in the core. DWAF species in Core PI-92-AR 39 range from the Gauss chronozone (Unit A) to the upper Matuyama (Unit J). Cyclammina pusilla has the most complete and longest range, followed by G. charoides and G. gordialis. The ranges of other species occur between the Gauss chronozone (Unit A) to the mid- Matuyama (Units D, E and F).

3. Core PI-92-AR 30 is the second youngest in the Canada Basin (base of core 1.2 Ma). DWAF range from the Jaramillo subchronozone (Matuyama, Unit G) at the base of the core, through the top of the Brunhes chronozone. Cyclammina pusilla

occurs from the Jaramillo (Unit G) to the mid Brunhes chronozone (Unit L). The stratigraphie ranges of A. polarensis is slightly longer than C. pusilla, however, it is not as complete, occurring from the Jaramillo subchronozone until the top of Unit L, bottom of Unit M. Trochammina lomonosovensis is recorded at the youngest point in the core, at the top of the Brunhes (mid-Unit M, see Chapter 5). The youngest of the cores. Core PI-92-AR 27 (base of core 1.1 Ma), ranges from the Matuyama through the Brunhes Chron. This is the case for Trochammina lomonosovensis, that has the longest range in the core. The dominant species,

Cyclammina pusilla has a relatively short range compared with other cores and is recorded from the Matuyama (Unit I) to the Brunhes (Unit L). Recurvoides contortus, Trochammina lomonosovensis = BB2, BBl (oxygen isotope Stage 1) are the youngest occurring on the Northwind Ridge, correlating from BB9 to BB 1 which represent interglacial periods (see Poore et al. in prep). The DWAF correlate with the interglacial/glacial cycles and have higher abundance values in the interglacial horizons.

8.4 Palaeoenvironment and Palaeoceanography

1. The main genera in the cores from the Eurasian and Canada Basins are

Cyclammina, Alveolophragmium, Trochammina, Glomospira, Rhabdammina, Psammosphaera. They inhabited a bathyal environment with the genera present living epifaunally, and were possibly affected by bottom currents. The absence of

DWAF from cores in both basins can be explained by the low fossilisation potential of some species and test destmction of fragile tests (see Schroder 1988).

2. The DWAF abundance indicated that the environment was affected by limited and variable organic flux, therefore large populations are not encountered throughout the cores. The DWAF had higher abundance values in the warmer interglacial periods when plotted against the stratigraphie models for the Eurasian Basin cores and Cores PI-92-AR 30 and PI-92-AR 27. This occurred because the interglacial periods would have been characterised by less ice cover at the surface. This would enable higher surface productivity with an increase of organic flux to the sea floor. The patterns exhibited by the DWAF indicated that their abundance is controlled by the amount of ice cover, surface productivity and the amount of organic flux to the sea floor. The role of water masses on DWAF distribution is complex, with the amount of data presented in this thesis not being sufficient to examine the role for the entire central Arctic Ocean.

8.5 Discussion and Overview

1. A detailed comparison with previous foraminiferal work is presented (Chapter 7). This is divided into work carried out on Recent and fossil sedimentary material from the central Arctic Ocean. The species discussed are summarised in tabular form. The agglutinated foraminifera found in previous studies of Recent sediment from both basins did not correspond well with those of this study. A reason for this is the loss of agglutinated species over time by destruction as result of them having a low preservation and fossilisation potential (see Schroder 1988).

2. In order to assess if there are any differences between the Eurasian and Amerasian Basin, the main species from the two core sets are compared using a fence diagram (Chapter 7). The DWAF show little difference between basins, with only age and ecological parameters, such as higher surface productivity during periods of reduced ice cover, explaining differences in occurrence or higher abundance.