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MARINE GEOLOGY INTERNATIONAL JOURNAl. OF MARINE GEOLOGE GEOCHEMISTRY AND GEOPHYSICS ELSEVIER Marine Geology 119 (1994) 269 285

Organic carbon, carbonate, and clay mineral distributions in eastern central Arctic Ocean surface sediments Ruediger Stein, Hannes Grobe, Monika Wahsner Alfred- Wegener-Institutefor Polar and Marine Research, Columbusstrafle, D-27515 Bremerhaven, Germany (Received January 27, 1993; revision accepted October 20, 1993)

Abstract

Results from a detailed sedimentological investigation of surface sediments from the eastern Arctic Ocean indicate that the distribution of different types of sediment facies is controlled by different environmental processes such as sea-ice distribution, terrigenous sediment supply, oceanic currents, and surface-water productivity. In comparison to other open-ocean environments, total organic carbon contents are high, with maximum values in some deep-basin areas as well as west and north of Svalbard. In general, the organic carbon fraction is dominated by terrigenous material as indicated by low hydrogen index values and high C/N ratios, probably transported by currents and/or sea ice from the Eurasian Shelf areas. The amount of marine organic carbon is of secondary importance reflecting the low-productivity environment described for the modern ice-covered Arctic Ocean. In the area north of Svalbard, some higher amounts of marine organic matter may indicate increased surface-water productivity controlled by the inflow of the warm Westspitsbergen Current (WSC) into the Arctic Ocean and reduced sea-ice cover. This influence of the WSC is also supported by the high content of biogenic carbonate recorded in the Yermak Plateau area. The clay mineral distribution gives information about different source areas and transport mechanisms. Illite, the dominant clay mineral in the eastern central Arctic Ocean sediments, reaches maximum values in the Morris-Jesup- Rise area and around Svalbard, indicating North Greenland and Svalbard to be most probable source areas. Kaolinite reaches maximum values in the Nansen Basin, east of Svalbard, and in the Barents Sea. Possible source areas are Mesozoic sediments in the Barents Sea (and Franz-Josef-Land). In contrast to the high smectite values determined in sea-ice samples, smectite contents are generally very low in the underlying surface sediments suggesting that the supply by sea ice is not the dominant mechanism for clay accumulation in the studied area of the modern central Arctic Ocean.

1. Introduction Ocean system and its relationship to global change has been slow in comparison to studies in other Although it is generally accepted that the Arctic ocean regions. This lack of knowledge is mainly Ocean (Fig. 1) is a very sensitive and important caused by the major technological/logistic prob- region for changes in the global climate, this region lems in reaching this permanently ice-covered is the last major physiographic province of the region with normal research vessels and in retriev- earth whose short- and long-term geological his- ing long and undisturbed sediment cores. The tory is not very well known. Since the first recovery available samples and data from the central Arctic and description of deep-sea sediments during the Basins are derived mainly from drifting ice islands famous 1893-1896 Fram-Expedition of Fridtjof such as T-3 (e.g., Clark et al., 1980) and CESAR Nansen (Nansen, 1897; B6ggild, 1906), the pro- (Jackson et al., 1985). In the eastern Arctic Basins, gress in getting a better understanding of the Arctic ship expeditions such as Ymer 80 (Fig. 2; Bostr6m

Fig. 1. Surface-watercirculation systems in the Arctic Ocean and occurrences of major coal deposits in the surrounding continents (from Bischofet al., 1990, based on Anon, 1978; Hale, 1990), supplemented by probable source areas of clay minerals in the Arctic Ocean. Letters/, K and S indicate the major clay mineral in a chlorite-illite-kaolinite-smectiteassociation (based on Darby, 1975; Naidu and Mowatt, 1983; Dalrymple and Maass, 1987; Elverhoi et al., 1989).

and Thiede, 1984) and Polarstern ARK-IV/3 Lomonosov Ridges, and the Morris-Jesup Rise (Fig. 2; Thiede, 1988) have greatly advanced our and the Yermak Plateau (Fig. 2; F~tterer, 1992). knowledge on Arctic Ocean paleoenvironments. The major objective of the Arctic 91 marine Comprehensive summaries about the present geology program is to study the paleoclimatic knowledge on Arctic Ocean geology are given by and paleoceanographic evolution of the Arctic Herman (1989), Bleil and Thiede (1990) and Ocean and its influence on the global Grantz et al. (1990). (paleo-)environment, including topics such as In 1991, an international and multidisciplinary changes in lithogenic, biogenic, and organogenic three-ship expedition (Arctic 91) has been carried sediment supply during glacial/interglacial cycles, out by the swedish Oden, the american Polar Star, glacial/interglacial variations in sea-ice cover, and and the German Polarstern. During this very suc- water-mass exchange between the Arctic and cessful expedition into the extreme central Arctic Atlantic Oceans, its global relevance and change Ocean area it was possible to recover onboard through time. In this paper, we present results Polarstern unique undisturbed surface sediments from a study of surface sediments taken during and long sediment cores from the Nansen, the 1991 Polarstern Expedition (FOtterer, 1992; Amundsen, and Makarov Basins, the Gakkel and Rachor, 1992) to point out the relationship R. Stein et al./Marine Geology 119 (1994) 269-285 271

160 ° 140 ° 120 °

75 ~

75 ° 0°

Fig. 2. Positions of surface sediment samples considered in the distribution maps of Figs. 3, 6 and 7. Sample positions are marked by triangles: Ymer-80 Expedition (Bostr6m and Thiede, 1984); open squares=Polarstern Expedition ARK-IV/3 (Thiede, 1988); circles=Polarstern Expedition ARK-VIII/2 (Rachor, 1992); and dots=Polarstern Expedition ARK-VIII/3 (ARCTIC '91) (FOtterer, 1992). between modern environmental processes and sedi- Ocean: the anticyclonic Beaufort Gyre in the ment accumulation in the eastern central Arctic Amerasian Basin and the Transpolar Drift in the Ocean. Eurasian Basin (Fig. 1). The latter, crossing our study area, is transporting sea ice from the Siberian shelf areas through the central Arctic to the Fram 2. Modern oceanography and environment Strait. Through Fram Strait, two major currents Today, two major current systems are domina- exchange water between the Arctic and the world ting the surface-water circulation in the Arctic ocean (Fig. 1). The cold, ice-transporting East 272 R. Stein et al./Marine Geology 119 (1994) 269~85

Greenland Current is the main current out of Ocean via the Transpolar Drift (Wollenburg, the Arctic Ocean. On the other hand, the 1991). In areas of extensive melting, sediment Westspitsbergen Current, an extension of the particles are released and deposited at the sea North Atlantic-Norwegian Current, carries warm, floor. In these areas, this process may dominate relatively saline water into the Arctic Ocean where the supply and accumulation of terrigenous mate- it cools down and extends in intermediate water rial in the polar environment. Icebergs are another depths into the eastern Arctic Basins (Aagard possibility for transportation of terrigenous mate- et al., 1985; Carmack, 1990). Of importance for rial into the central Arctic, but are very rare today the thermohaline circulation in the Arctic Ocean due to the absence of large ice shelves. Source is the formation of brines on polar shelves, i.e., areas for icebergs today are Ellesmere Island, cold, saline, and well-oxygenated water masses North Greenland, Svalbard, Franz-Josef Land, which sink over the continental margin into the and Severnaya Zemlya (Sudgen, 1982; Darby et al., deep basins (Aagard et al., 1985). The export of 1989). A detailed study of the composition and sea ice through Fram Strait and its melt in the grain size of the siliciclastic sediment fractions Greenland Norwegian Sea as well as the deep- might give an important key to distinguish between water exchange between Arctic and Atlantic seem different source areas and transport mechnisms to play an important role in controlling the deep- (see below). water formation in the northern North Atlantic and, thus, is of global significance (Untersteiner and Carmack, 1992). 3. Methods Another important phenomenon of the Arctic Ocean is the permanent sea-ice cover with its During Polarstern cruises ARK-VIII/2 and strong seasonal variation in the marginal (shelf) ARK-VIII/3 (Arctic 91), surface and near-surface areas. This sea-ice cover has a distinct influence samples were taken by means of giant box corer on marine biota, oceanic circulation, and surface (GKG) and multicorer (MUC), and long sediment albedo, which all are major controls on climatic cores were taken by a kastenlot corer, a giant change. Although mean primary productivity of piston corer, and a gravity corer (Ft~tterer, 1992; the central Arctic Ocean is very low because of Rachor, 1992). Cores were collected from about the sea-ice cover, productivity might be very high 60 geological stations in the eastern Arctic Ocean at the ice edge because of supply of nutrients (Fig. 2). On these sediments, a detailed sedimento- during melting phases and ice edge upwelling, logical and geochemical investigation program has resulting in phytoplankton blooms (Subba Rao been started. Data produced on the surface sedi- and Platt, 1984; Sakshaug and Skjoldal, 1989). ments (0-1 cm) are presented and discussed in Since surface-water productivity may affect the this paper. concentration of atmospheric CO2 (i.e., in areas Total carbon, total nitrogen, and total organic of high production rate of organic matter, the carbon contents were determined on ground bulk ocean may act as a sink for CO2) which is an samples and HCl-treated carbonate-free samples, important factor controlling the global climate, respectively, using a HERAEUS CHN analyser the quantification of the organic carbon budget in and a LECO-CS analyser. Carbonate contents the Arctic Ocean is also of major significance for were calculated as: understanding the global climate system. (total carbon-total organic carbon) × 8.333 A large proportion of the sea ice is "dirty ice" containing high amounts of sediment (Pfirman Rock-Eval pyrolysis was performed according to et al., 1989; Wollenburg 1991; Ftitterer, 1992; the method described by Espitali6 et al. (1977). Nt~rnberg et al., 1994-this volume). Most of the Kerogen microscopy was performed on polished, sediment is incorporated into the sea ice in the epoxy-impregnated blocks of sediment; the macer- Siberian shelf areas and then transported as ice- als were classified according to the nomenclature rafted debris (IRD) through the central Arctic described by Stach et al. (1982). R. Stein et al./Marine Geology 119 (1994) 269-285 273

Samples used for grain size (of the carbonate- Amundsen and Nansen Basins as well as directly free sediment fraction) and clay mineral analyses north of Svalbard. Carbonate contents of l0 to were treated with acetic acid to dissolve the carbon- 20% are common on the Yermark Plateau, the ate, oxidized and disaggregated by means of a Gakkel Ridge, and the eastern flank of the 3-10% H20 2 solution, and wet-sieved through a Lomonosov Ridge. Maximum carbonate contents 63 #m sieve. From the <63/~m fraction, the silt are recorded on the Morris-Jesup Rise, reaching (2-63/~m) and clay (<2/~m) fractions were sepa- values of up to 30%. One single value of 38% was rated using settling tubes ("Atterberg method"; measured on a sample from the northwestern Mfiller, 1967). From the clay fraction, texturally- Svalbard continental margin. There is no correla- oriented specimens were produced by vacuum tion between carbonate content and water depth filtration through a filter of 0.15/~m pore size (Fig. 4). (Lange, 1982). These specimens were then ana- lyzed by means of a Philips 1700 X-Ray diffraction 4.2. Distribution and composition of organic carbon system with a cobalt K~-radiation. The measure- ments were performed on untreated and glycolated Almost all of the surface sediment samples have (18 hours at 60°C) samples, both from 2 ° to 40 ° relatively high total organic carbon (TOC) values 2® in 0.02 ° steps for 2 seconds at each step. For ranging between about 0.5 and 2% (Table 1; Figs. separation of the kaolinite/chlorite 7 ,& peak, an 3C and 4). Maximum values of > 1% occur around additional scan was performed in 0.005 ° steps for northern Svalbard and in the central Nansen Basin, 2 seconds at each step between 28 ° and 30.5 ° 2 O low values are typical for the Gakkel Ridge, the in order to determine the 3.54 A peak of chlorite eastern flank of the Lomonosov Ridge, and the and the 3.58 A peak of kaolinite (Biscaye, 1965). Morris-Jesup Rise. In general, TOC values are Semiquantitative evaluations were based on peak higher in the deep-sea basins than on the ridges. areas of the four clay minerals smectite (~ 17 ]~), There is, however, no simple linear correlation illite (10 A), kaolinite (7 and 3.57 A), and chlorite between TOC content and water depth (Fig. 4). (7 and 3.54 A,) (Biscaye, 1965). To get informations about the composition of the organic matter, hydrogen index values and C/N ratios have been determined. In immature 4. Results sediments, hydrogen indices of < 100 mgHC/gC are typical of terrigenous organic matter (kerogen Carbonate and organic carbon contents, type III), hydrogen indices of 300 to 800 mgHC/gC hydrogen index values and temperatures of are typical of marine organic matter (kerogen maximum pyrolysis yield (Tmax values) derived types I and II) (e.g., Tissot and Welte, 1984). C/N from Rock-Eval pyrolysis, organic carbon/ ratios of marine organic matter are around 6 nitrogen (C/N) ratios, sand-silt-clay contents of whereas terrigenous organic matter has C/N ratios carbonate-free samples, and the clay mineral com- of >15 (e.g., Bordowskiy, 1965; Hedges et al., position determined on all surface sediment 1986). For more precise determinations of the samples are summarized in Tables 1 and 2. marine and terrigenous proportions of the Carbonate and organic carbon contents were organic carbon fraction, other methods such as determined on surface sediment samples taken by kerogen/coal petrography and gaschromatography both multicorer and giant box corer. are required. These more time-consuming investigations are in progress on Arctic 91 material 4.1. Carbonate distribution (Schubert and Stein, in prep.). Based on low hydrogen index values of < 100, In general, the carbonate content of the surface the organic carbon fraction of the central Arctic sediments is relatively low; most values are less Ocean surface sediments is clearly dominated by than 10% (Table 1; Figs. 3A and 4). Minimum terrigenous material (kerogen type III) (Table 1; values of less than 5% occur in the central Figs. 3C and 5). This is also corrobarated by 274 R. Stein et al./Marine Geology 119 (1994) 269-285

Table 1 Summary table of core number, longitude/latitude, water depth (m), carbonate and total organic carbon contents (%), C/N ratios, hydrogen index values (mgHC/gC), and Tm~x values (°C). For most of the ARK-VIII/3 samples (i.e., Cores 2157-2215) carbonate and organic carbon data have been determined on both giant box corer (GKG) and multicorer (MUC) surface sediment samples

Core Long. Lat. Depth CaCOs CaCO3 TOC TOC HI Tmax C/N (m) (GKG) (MUC) (GKG) (MUC)

2111 34.877 76.638 218 2.87 1.45 2113 34.898 76.003 260 2.98 1.40 158 411 2114 19.092 77.568 178 5.66 2.13 159 423 2115 18.328 77.200 101 5.03 1.75 109 423 2116 17.168 75.988 331 9.55 1.53 144 420 2117 5.994 79.008 202 12.05 1.02 113 414 2119 8.160 79.002 897 8.00 1.00 183 365 2120 8.592 79.027 175 14.00 1.41 174 410 2121 10.743 79.018 337 11.22 1.75 133 400 2122 7.543 80.390 702 4.20 1.17 147 368 2123 9.857 80.167 574 4.40 1.41 147 408 2124 11.202 79.970 172 5.00 0.17 2125 12.237 80.047 94 38.30 0.42 247 393 2127 18.457 81.020 195 5.50 0.35 137 406 2128 16.707 81.507 2528 9.00 0.81 135 344 2129 17.472 81.367 861 3.40 0.75 174 381 2130 18.623 81.290 550 8.00 1.57 132 413 2131 27.098 80.975 106 3.70 0.35 122 382 2132 31.488 81.443 236 7.70 0.63 106 404 2133 30.780 81.432 399 7.80 0.73 100 421 2134 29.803 81.680 2440 9.00 1.41 117 414 2136 30.550 81.525 1947 6.50 0.82 110 383 2137 30.777 81.578 1394 5.00 0.91 118 403 2138 30.593 81.535 862 6.30 1.08 108 386 2142 30.635 80.848 116 13.40 0.43 155 425 2143 30.120 80.812 197 4.80 0.89 161 405 2t44 29.473 80.747 505 5.70 1.36 143 353 2147 29.136 80.336 380 5.40 0.80 131 376 2148 29.603 80.013 339 5.60 1.30 148 395 2149 31.733 73.176 77 3.10 0.48 185 423 2150 32.134 78.666 283 4.40 1.26 196 513 2151 32.939 77.991 143 2.70 0.81 183 418 2153 34.810 76.608 187 4.70 1.42 172 4OO 2156 30.230 80.087 258 6.20 1.19 138 4OO 2157 29.915 81.755 2874 11.30 5.70 1.33 1.89 89 421 10 2158 29.925 82.776 3800 12.10 0.88 57 386 2159 30.370 83.960 4055 10.40 8.80 0.75 0.94 62 392 26 2160 37.951 84.881 4029 0.00 1.12 120 518 28 2161 44.422 85.450 4005 2.60 0.00 0.78 1.1 97 477 28 2162 50.827 85.795 3981 2.90 0.76 142 5O2 2163 59.215 86.242 3040 8.30 7.50 0.47 0.54 55 371 19 2164 59.176 86.338 2004 8.30 7.20 0.33 0.24 46 404 13 2165 59.960 86.447 2011 8.90 11.30 0.26 0.4 62 378 23 2166 59.699 86.860 3618 6.30 5.10 0.52 0.56 73 377 20 2167 59.015 86.945 4434 2.70 1.70 0.31 0.49 108 522 21 2168 55.934 87.510 3846 4.70 5.30 0.45 0.52 76 349 22 2170 60.766 87.590 4226 5.80 5.60 0.55 0.68 47 360 24 2171 68.977 87.586 4384 6.20 5.90 0.60 0.71 71 359 19 2172 68.377 87.257 4384 6.40 5.60 0.54 0.69 75 326 18 2174 90.500 87.495 4427 4.10 3.60 0.63 0.72 84 432 21 IL Stein et al./Marine Geology 119 (1994) 269-285 275

Table 1 (continued)

Core Long. Lat. Depth CaCO3 CaCO3 TOC TOC HI Tin.x C/N (m) (GKG) (MUC) (GKG) (MUC)

2175 103.566 87.568 4378 4.30 3.20 0.66 0.77 76 472 27 2176 108.750 87.765 4361 3.80 2.80 0.74 0.87 88 522 22 2177 134.926 88.036 1388 6.20 5.40 0.63 0.62 79 421 16 2178 159.168 88.005 4009 5.80 6.60 0.40 0.43 60 399 15 2179 138.029 87.746 1230 5.90 6.00 0.54 0.6 88 379 16 2180 156.676 87.626 4005 6.30 0.40 72 369 2181 153.059 87.596 3112 9.80 24.00 0.32 0.21 57 403 9 2182 151.120 87.572 2489 15.30 12.20 0.30 0.29 55 393 17 2183 148.830 87.602 2016 6.70 8.40 0.23 0.21 80 398 11 2184 148.140 87.611 1640 11.70 10.50 0.25 0.27 44 398 7 2185 144.166 87.529 1073 8.60 9.20 0.49 0.56 60 385 12 2186 139.907 88.512 1867 10.00 6.50 0.58 0.75 65 382 10 2187 126.913 88.735 3819 3.10 1.70 1.00 1.2 8l 390 10 2189 144.550 88.781 1001 10.70 11.60 0.37 0.41 129 450 13 2190 90.000 90.000 4240 3.30 1.80 0.91 1.12 75 479 11 2191 9.011 88.991 4346 8.10 0.73 57 348 20 2192 9.857 88.260 4375 10.00 8.50 0.56 0.68 52 346 19 2193 11.475 87.512 4399 6.40 5.10 0.67 0.73 64 427 19 2194 7.488 86.593 4326 11.80 0.52 57 353 2195 9.617 86.253 3793 7.80 0.61 63 360 2196 0.165 85.962 3958 8.00 6.50 0.64 0.57 49 391 6 2198 -9.057 85.565 3820 8.90 10.50 0.57 0.44 47 400 10 2199 - 11.913 85.435 1789 12.20 0.30 2200 - 14.022 85.328 1073 23.30 21.10 0.31 0.35 51 388 8 2202 - 14.369 85.109 1081 29.00 28.00 0.25 0.34 44 410 5 2204 - 13.035 85.058 3899 10.70 0.7 77 386 7 2205 -6.767 84.644 4283 6.90 6.90 0.40 0.47 74 526 7 2206 -2.505 84.278 2993 7.40 0.86 67 359 7 2208 4.603 83.640 3681 8.60 0.8 70 364 9 2209 8.573 83.225 4046 13.30 0.95 64 383 2210 10.125 83.045 3949 13.50 17.10 0.89 0.87 58 371 11 2212 15.672 82.024 2531 13.70 13.70 1.15 63 400 2213 8.205 80.473 897 3.40 2.40 1.16 1.42 147 483 10 2214 6.627 80.269 552 3.40 3.70 0.83 0.87 208 380 11 2215 5.341 79.695 2045 4.90 6.30 0.65 0.55 136 390 10

dominantly high C/N ratios (Table 1). Sediments dark gray siltstones (i.e., IRD) with TOC contents from the northern Svalbard Continental Margin of almost 4% resulted in hydrogen index values show some higher hydrogen index values of 100 < 20 and Tmax values around 500°C, indicating the to 250 suggesting the preservation of some higher higher maturity of this material. amounts of marine organic material (Figs. 3C and 5). 4.2. Grain-size distribution Most of the organic matter is immature as indicated by low Tma~ values of less than 435°C Because the carbonate content of most of the (cf. Espitali6 et al., 1977; Tissot and Welte, 1984). surface samples is relatively low (Table 2; Fig. 3A), In several samples, Tmax reach values higher than the grain-size distribution of the carbonate-free 450°C suggesting the presence of more mature sediment fraction (Fig. 6) was used to classify the reworked organic matter (Table 1; Fig. 5). Rock- central Arctic surface sediments as mainly silty Eval pyrolysis performed on single pebble-sized clay or clayey silt. This is similar to sediments in 276 R. Stein et al./Marine Geology 119 (1994) 269-285

,RE.~., I ~DEX] ~)

2.E 5- 0." !~00 5- 3- ) - 150 I O- 5- 150 J __ >2 >1

Fig. 3. Distribution maps of carbonate (A), total organic carbon (B), and hydrogen indices (C). In the carbonate and organic carbon maps data from Bostr6m and Thiede (1984) and Pagels (1991) are included (open squares).

SURFACE SEDIMENTS the sand content shows values below 10%. The silt 0 =~ • • 0 8 ° ° • fraction has lowest values north of Svalbard; maxi-

o ° e • • • mum values occur on the Yermak Plateau, the -1000 • , -1000 ," • ,,- Gakkel Ridge and the eastern flank of the

L •= ,-r -2000 ~ ~ : -200G ~- • Lomonosov Ridge (Fig. 6B). In general, the sedi- I- | • • • ments have a distinctly higher clay content in the -3000 - . -3000 . = basins of the Arctic Ocean than on the ridges I- ,< • • ee= o° w (Fig. 6C). This is particularly clear in the -4000, e , -4000 • • % .••.b -'.q, • Amundsen Basin where the clay fraction shows values of more than 60% (with a maximum of up -5000 -5000 0 10 20 30 0 1 2 to 80%). The clay fraction is therefore a very CARBONATE (%) TOTAL ORGANIC CARBON (%) important component of Arctic deep-sea sedi- Fig. 4. Variations of carbonate and total organic carbon ments. The most drastic variations in the contents vs. water depth of ARK-VIII/2 and ARK-VIII/3 grain-size distribution exist on the Morris-Jesup- (Arctic 91) surface sediments. Rise and on the Svalbard Continental Margin (Table 2; Fig. 6). the western Arctic Ocean (Clark et al., 1980). Only a few samples from the continental margin as well 4.3. Clay-mineral distribution as the Gakkel and Lomonosov Ridges have a higher sand content (sandy silt) (Fig. 6A). The In all surface sediments illite is the dominant highest sand content occurs in the samples from clay mineral with concentrations between 40 and the Morris-Jesup Rise and on the continental 70% (Table 2; Fig. 7A). The highest illite contents margin north of Svalbard. In the deep-sea basins, occur north of Svalbard and on the Morris-Jesup- R. Stein et al./Marine Geology 119 (1994) 269 285 277

SURFACE SEDIMENTS 20% (Table2; Fig. 7C). Concentrations of less 500 o ARK VIII/2 than 5% occur around Svalbard and on the Morris- • ARK VIII/3 Jesup-Rise. The highest smectite concentrations O 400 (up to a maximum of 20%) were determined on b the Lomonosov Ridge. E v 300- X LU Q 5. Discussion Z Jl o i j -- 200- Z O ILl o 0 0 CI~ 5.1. Carbonate content o o o-°~o~ \ • o reworked? o 0 o^ • ~o' •\ A rr 100- In pelagic sediments, variations in biogenic car- >. "t- bonate content are mainly controlled by dissolution, dilution, and/or productivity changes. Based O J 300 400 soo'k on coarse fraction data, the carbonate in the Tmax (oC) ~t~ modern eastern central Arctic Ocean sediments (Fig. 3A) is mainly of biogenic origin; detrital Coal Fragments Dark Grey Silt/Claystones carbonate is only of minor importance. Planktonic (Man Macera s: Vitrinite, Inertinite) foraminifers are dominant throughout, whereas benthic foraminifers, bivalves, and ostracodes Fig. 5. Results of Rock-Eval pyrolysis of surface sediment occur in minor amounts on the ridges and plateaus samples of ARK-VIII/2 and ARK-VIII/3 Expeditions, pre- (F~tterer, 1992). Coccoliths are also present in sented in a hydrogen index vs. Tmax diagram (cf. Espitali6 significant amounts in the surface sediments (Gard, et al., 1977; Tissot and Welte, 1984). Field III indicates 1993). The occurrence of planktonic foraminifera terrigenous organic matter ("kerogen type III"), fields I and H indicate marine organic matter ("kerogen types I and II"). and coccoliths suggests at least seasonal open-ice conditions. The generally low content of detrital carbonate Rise. The lowest illite concentrations exist on the in the eastern central Arctic Ocean may indicate Barents Sea Shelf and in the central Nansen Basin that the supply of IRD from the western Arctic is north of Franz-Josef-Land. In all samples, the illite not of major importance today. Only in the is very well crystallized, with a half-height width Morris-Jesup Rise area, i.e., relatively close to the of about 0.3A°2®. North Greenland continental margin, major pro- The average chlorite concentration in the surface portions of detrital calcite and dolomite grains sediments is about 22%; only a very few samples were recorded (Vogt and Stein, unpubl, data). show values less than 20% or more than 25% This may support the transport of terrigenous (Table 2). The few sediments with chlorite concen- (carbonate) sediments from northern Greenland trations of more than 25% are located on the onto the Morris-Jesup Rise, the source area of Gakkel Ridge. No significant regional variations which are probably the Paleozoic carbonate rocks in chlorite content is apparent. in North Greenland (Peel, 1982). This preliminary The kaolinite values vary between 10 and 40% interpretation has to be proven, however, by a (Table 2; Fig. 7B). Samples with more than 20% more quantitative coarse fraction analysis. are located in the Nansen Basin northwest of The good preservation of foraminifera tests in Franz Josef Land and on the Barents Sea all surface sediment samples from about 200 to Continental Margin north of Svalbard. North of almost 4500 m water depth suggests that carbonate the Gakkel Ridge, kaolinite contents are less dissolution has not dominantly controlled the car- than 20%. bonate variations shown in Fig. 3A; instead, dilu- In comparison to the other clay minerals, smec- tion by siliciclastics seems to be more important. tite contents are low and vary between < 5% and This is in agreement with results of investigations ~J

8 ~

eb~

5 i ~

7~ o~ R. Stein et al./Marine Geology 119 (1994) 269-285 279

Table 2 (contmued)

Station no. Depth (m) Sand Silt Clay Smectite Illite Chlorite Kaolinite

2178-2 4009 7 48 46 6 59 24 10 2179-1 1230 3 43 55 8 51 26 15 2180-1 4005 8 47 45 8 59 22 12 2181-3 3112 15 55 30 8 59 22 12 2182-1 2489 30 47 24 8 54 25 13 2183-2 2016 38 41 20 8 53 23 16 2184-1 1640 24 51 25 9 55 23 13 2185-3 1073 9 43 48 16 51 22 11 2186-1 1867 8 61 30 10 52 24 14 2187-1 3819 0 38 61 8 50 26 16 2189-1 1001 34 47 19 11 49 24 16 2190-3 4240 1 33 67 14 49 23 14 2192-1 4375 1 29 70 5 63 22 10 2193-2 4399 2 73 25 2 60 22 15 2194-1 4326 1 54 45 1 63 24 13 2195-4 3793 3 38 59 11 54 22 13 2196-2 3958 2 36 62 9 55 23 13 2198-1 3820 13 37 50 6 61 22 12 2199-4 1789 96 3 1 7 57 24 12 2200-2 1073 35 38 27 1 67 21 10 2202-2 1081 46 32 22 3 64 21 12 2205-3 4283 0 39 61 7 53 22 18 2209-1 4046 1 44 55 8 56 20 16 2210-1 3949 3 52 45 9 53 21 16 2212-5 2531 3 83 14 1 60 23 17 2213-1 897 9 47 44 7 54 23 16 2214-1 552 29 54 18 7 56 21 16 2215-2 2045 65 24 11 8 57 17 17

of carbonate dissolution on planktonic foramini- available until now. Distribution maps of total fera tests from the eastern central Arctic Ocean organic carbon and carbonate in Arctic Ocean (Pagels, 1991). Based on these results, the modern surface sediments north of Svalbard up to 86°N lysocline of this area is at about 4700 m water has been produced by Pagels (1991) (based on his depth. In the Yermak Plateau area the high carbon- own data and data from Snare (1985) and ate values may additionally reflect the influence of Markussen (1986)). The results of Bostr6m and the warm Westspitsbergen Current, as already Thiede (1984) and Pagels (1991) agree well with suggested by Pagels ( 1991 ). our data and are included in the maps of Fig. 3A and B. Data on the quantity and quality of the 5.2. Organic carbon record." Productivity indicator organic carbon fraction (and clay minerals) are vs. terrigenous supply determined for the Fram Strait area, i.e., for the area directly south of our study area, and presented Data on amount and composition (i.e., marine in distribution maps by Hebbeln and Berner vs. terrigenous) of the organic carbon fraction in (1993). Both data sets fit together very well. marine sediments can yield important information In general, the modern eastern Arctic Ocean is about the depositional environment, oceanic circu- a low-productivity environment because of its sea- lation, and surface-water productivity (e.g., Stein, ice coverage (Subba Rao and Platt, 1984). This, 1991, and further references therein). In the central together with the well-oxygenated deep-water Arctic Ocean, this kind of detailed data was not sphere, results in the very low flux and preservation 280 R. Stein et al./Marine Geology 119 (1994) 269-285

5 5

- 50 1t 2

Fig. 6. Distribution maps of sand (A), silt (B), and clay (C) contents of the carbonate-free sediment fractions.

A ~ B I KAouNtT~~ I C I sMEeTITE~1

Fig. 7. Clay mineral distribution maps of surface sediments. (A) Illite, (B) kaolinite, and (C) smectite. R. Stein et al./Marine Geology 119 (1994) 269-285 281 of marine organic matter in the surface sediments. as shown in numerous studies from different parts However, the occurrence of significant amount of of the world ocean (e.g., Sarnthein et al., 1982; biogenic carbonate (see above) as well as the Naidu and Mowatt, 1983; Stein and Robert, 1985; occurrence of detectable amounts of unsaturated Cremer et al., 1989; Chamley, 1989, and further alkenones (Schubert and Stein, unpubl, data) references therein). In polar and subpolar regions which are biomarker produced by prymnesio- where physical weathering processes dominate and phytes (e.g., Marlowe et al., 1984), indicate at chemical and diagenetic alterations are negligible, least seasonal open-ice or ice-free conditions and the clay mineral association in marine sediments some bioproductivity. can be a valuable indicator of sediment sources. The relatively high organic carbon contents, i.e., In general, the clay mineralogy of Arctic Ocean values which are distinctly higher than those sediments reflects the source mineralogies of the recorded in modern normal open-marine environ- landmasses and shelf areas surrounding the central ments, are certainly caused by the supply of terrige- Arctic Ocean basins (Darby et al., 1989 and further nous organic matter. This is clearly indicated by references therein): Illite is the dominant clay the low hydrogen index values (Figs. 3C and 4), mineral (mostly > 50%), followed by chlorite and generally high C/N ratios (Table 1 ) as well as first kaolinite (5 to 30%); smectites are variable, but of results of kerogen/coal microscopy work (Fig. 4). minor importance. This general picture is valid for Part of the organic carbon measured in ground the Amerasian Basin (e.g., Naidu et al., 1975; bulk sediments derives from black organic-carbon- Clark et al., 1980; Dalrymple and Maass, 1987, rich silt stones (up to 4"/0 TOC) and coal fragments Darby et al., 1989) as well as the Eurasian Basin which were identified as IRD in the coarse fraction. (Table 2; Fig. 7; cf. Berner 1991). However when These particles as well as the other terrigenous going into details, differences in clay mineral asso- organic material were probably derived from the ciations between different source areas are obvious Siberian shelf areas and were transported by sea and can be used as source rock indicators (Fig. 1). ice (via the Transpolar Drift) and/or currents (cf. For example, potential source areas for kaolinite Pfirman et al., 1989; Wollenburg, 1991; Bischof in Arctic Ocean sediments are Mesozoic and et al., 1992). Cenozoic strata along the north coast of Alaska Increased organic carbon contents and increased and Canada (Darby, 1975; Naidu and Mowatt, hydrogen index values were recorded in the sedi- 1983; Dalrymple and Maass, 1987) and in the ments around Northwest Svalbard (Fig. 3B and Barents Sea area (Birkenmajer, 1989; Elverhoi C), indicating increased preservation of marine et al., 1989). A source for smectite is the Laptev organic matter in this area. These increased marine Sea shelf area (Wollenburg, 1991; Ntirnberg et al., organic carbon values are probably caused by 1994-this volume). Locally smectite-rich Mesozoic increased (ice-edge) surface-water productivity due strata are out-cropping on eastern Svalbard and to reduced sea-ice cover and increased nutrient in the Barents Sea (Elverhoi et al., 1989). The supply, both triggered by the inflow of warm high smectite value of 20%° recorded at Barents Atlantic Ocean water masses, i.e., the Sea Core PS2113 (Table2) might be related to Westspitsbergen Current. such a smectite-rich source. The maximum illite concentration north of 5.3. Clay minerals and grain size." Sources and Svalbard and on the Morris-Jesup Rise (Fig. 7A) transport mechanisms support the idea that illite is transported from northern Greenland and from Svalbard into the Records on clay-mineral composition and grain- Arctic Ocean (Fig. 1). Transport of terrigenous size distribution determined in marine sediment sediments from northern Greenland onto the cores might give important information about Morris-Jesup Rise is also suggested from the occur- different source areas and transport mechanisms rence of sand-sized grains of detrital carbonate of the terrigenous material as well as the climate (see above). of the source area and their changes through time, Based on the distribution map of kaolinite, 282 R. Stein et al./Marine Geology 119 (1994) 269-285 probable source areas for kaolinite are the Barents ice. The surface sediments of the Eurasian Basin, Sea shelf area and Franz-Josef-Land (Figs. 1 and however, have only very low contents of smectite 7B; Berner, 1991). Cold, saline, dense water (Figs. 7C and 8; Berner 1991). This indicates that formed on the shelf, may sink over the continental sea ice is not the dominant transport mechanism margin into the Nansen Basin (Aagaard et al., for clay-sized material in the Eurasian Basin, as 1985) and carry kaolinite-rich suspension down proposed by Wollenburg (1991). Other transport into the deep-sea environment. Important trans- mechanisms such as oceanic and turbidity currents port tracks for the suspension-rich water masses are probably more important in controlling the might be the major troughs northwest and north- sedimentation for most parts of our study area east of Svalbard. Turbidity currents are another today. If terrigenous sediments are delivered pri- common transport mechanism of clay-rich suspen- marily by sea ice, on the other hand, then only the sions from the Arctic shelves into the deep basins. coarser (silt- and sand-sized) material is accumu- This is supported by the occurrence of a large lated inplace whereas the clay-sized material is number of clayey-silty distal turbidites recorded transported/winnowed by oceanic currents. This in the Nansen and Amundsen Basins (Ftitterer, could explain why the clay mineral signal does not 1992). reflect the IRD supply. The high content of terrige- Sediments from sea ice sampled at the same nous silt on the ridges supports this also. In the locations as surface sediment samples have high basins, on the other hand, the IRD signal is smectite contents of 15 to 60% similar to surface masked by fine-grained turbidites. A detailed sediments from the Laptev Sea shelf which contain heavy-mineral analysis of central Arctic Ocean up to 45% smectite (Fig. 8; Wollenburg, 199; sediments will probably yield more information Niarnberg et al., 1994-this volume). This suggests about the importance of IRD input via the that the Laptev Sea shelf is the potential source Transpolar Drift than a clay mineralogy study area of the siliciclastic material included in the sea does, because very specific heavy minerals (e.g.,

Smectlte (%)

45 o 40 + \ ~ ooo

35 ~ I ° A +llo o o o o o o Arctic see ice sediments 30 II o eo +~ll °° + Leptev Sea surface 2s S sediments ! \ oo °°°°°° °° o o 2O I \ Barents See surface ÷/ \ o °° o •ediments 15 • Arctic surface sediments e. :• 10 \ 6 • • /. \ o i .'T:'~t f 4 ~' i I 0 5 10 15 20 25 30 35 40 Kaolinite (%)

Fig. 8. Smectite versus kaolinite diagram. Four major fields of different smectite-kaolinite provinces have been distinguished. (A) Sea-ice sediments (data from Wollenburg, 1991; Niirnberg et al., 1994-this volume); (B) Laptev Sea surface sediments (data from Nfirnberg etal., 1994-this volume); (C) Barents Sea surface sediments (data from Table 2); (D) Arctic Ocean surface sediments (data from Table 2). R. Stein et al./Marine Geology 119 (1994) 269-285 283 epidote, pyroxene, etc.) characterize the source Alfred-Wegener-Institute for Polar and Marine sediments in the Laptev Sea area (Korolev, pers. Research. commun., 1993).

6. Summary References

Data on carbonate, organic carbon, grain size, Aagaard, K., Swift, J. and Carmack, K., 1985. Thermohaline and clay minerals of surface sediments give impor- circulation in the Arctic Mediterranean Seas. J. Geophys. tant information about the depositional environ- Res., 90: 4833-4846. Anderson, L.G. and Carlsson, M.L., 1991. Swedish Arctic ment, oceanic circulation patterns, and surface- Research Programm 1991, International Arctic Ocean water productivity in the modem eastern central Expedition 1991. Icebreaker Oden Cruise Rep., Swed. Pol. Arctic Ocean and can be summarized as follows: Res. Secret., Stockholm, 128 pp. (1) Carbonate contents are generally less than Anon, 1978. Polar Regions Atlas. Produced by the Foreign 10%, with higher values typical for the ridges and Assessment Center, Central Intelligence Agency. Berner, H., 1991. Mechanismen der Sedimentbildung in der lower values typical for the basins. The carbonate Framstrasse, im Arktischen Ozean und in der Norwegischen is mainly of biogenic origin; significant amounts See. Ber. Fachbereich Geowiss. Univ. Bremen, 20, 167 pp. of detrital carbonate were only recorded in the Birkenmajer, H., 1989. The geology of Svalbard, the western Morris-Jesup-Rise area. part of the Barents Sea, and the continental margin of (2) Organic carbon contents vary between 0.5 Scandinavia. In: A.E. Nairn et al. (Editors), The Ocean Basins and Margins. (The Arctic Ocean, 5.) Plenum, New and 2% and are mainly of terrigenous origin. York, pp. 265-329. Higher amounts of marine organic matter are only Biscaye, P.E., 1965. Mineralogy and sedimentation of recent preserved in the area north of Svalbard indicating deep-sea clays in the Atlantic Ocean and adjacent seas and at least occasionally open-ice or ice-free conditions oceans. Geol. Soc. Am. Bull., 76:803 832. and increased surface-water productivity due to Bischof, J., Koch, J., Kubisch, M., Spielhagen, R.F. and Thiede, J., 1990. Nordic Seas surface ice drift reconstructions: the influence of the warm Westspitsbergen Current. evidence from ice rafted coal fragments during oxygen (3) Illite is mainly supplied from the northern isotope stage 6. In: J.A. Dowdeswell and J.D. Scourse Greenland and Svalbard areas. Kaolinite has its (Editors), Glacimarine Environments: Processes and origin in the Barents Sea and Franz-Josef-Land Sediments. Geol. Soc. Spec. Publ., 53:235 251. areas. Smectite, a major clay mineral in sediments Bleil, U. and Thiede, J., 1990. Geological History of the Polar Oceans: Arctic versus Antarctic. (NATO ASI Ser. C.) of the Laptev Sea shelf (the major source area of Kluwer, Dordrecht, 308, 823 pp. the IRD) as well as sea-ice samples, is of minor Bordowskiy, O.K., 1965, Sources of organic matter in marine importance in the eastern central Arctic Ocean basins. Mar. Geol., 3:5 31. surface sediments. B6ggild, O.B., 1906. On the bottom deposits of the north polar seas: Scientific results of the Norwegian North Polar Expedition 1893-1896. 5, pp. 1 62. Bostr6m, K. and Thiede, J., 1984. YMER-80. Swedish Arctic Acknowledgments Expedition Cruise Report. Meddel. Stockholms Univ. Geol. Inst., 260, 123 pp. For technical assistance and data discussion we Carmack, E., 1990. Large-Scale Physical Oceanography of thank R. Petscheck, H. R6ben, C. Schubert, M. Polar Oceans. In: W.O. Smith (Editor), Polar Oceanography, Part A, Physical Science. Academic Press, San Diego, Seebeck and R. Stax. The captain and the crew of pp. 171-222. the R.V. Polarstern are gratefully acknowledged Chamley, H., 1989. Clay Sedimentology. Springer, Berlin, for cooperation during the expedition ARK VIII/3. 623 pp. We also thank two anonymous reviewers for their Clark, D.L., Whitman, R.R., Morgan, K.A. and Mackay, constructive suggestions for the improvement of S.D., 1980. Stratigraphy and glacio-marine sediments of the Amerasian Basin, central Arctic Ocean. Geol. Soc. Am. the manuscript. Financial support was provided Spec. Pap., 181, 57 pp. by the Deutsche Forschungsgemeinschaft (grant no. Cremer, M., Maillet, N. and Latouche, C., 1989. Analysis of STE 412/6). This is contribution No. 702 of the sedimentary facies and clay mineralogy of the Neogene- 284 R. Stein et al./Marine Geology 119 (1994) 269-285

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