Supplement of Clim. Past, 11, 1507–1525, 2015 http://www.clim-past.net/11/1507/2015/ doi:10.5194/cp-11-1507-2015-supplement © Author(s) 2015. CC Attribution 3.0 License.
Supplement of Stratification of surface waters during the last glacial millennial climatic events: a key factor in subsurface and deep-water mass dynamics M. Wary et al. Correspondence to: M. Wary (
[email protected])
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Why interpreting the reconstructed planktonic foraminiferal temperature signal as relative subsurface temperature variations is coherent in our study area?
In the present study, we reconstruct oceanic temperatures by applying a transfer function to planktonic foraminifera assemblages. This transfer function uses a modern database where annual and seasonal oceanic temperatures are extracted at 10 meters water depth. In such a configuration, the reconstructed temperatures are, or should be a priori, assumed to represent sea-surface temperatures (SST). However, the comparison of our foraminifera-derived temperature (F-Temp) signals with our dinocyst-derived SST signals (reconstructed by applying a similar transfer function to dinocyst assemblages) shows strong discrepancies. Studies dealing with SST reconstructions obtained through different methods (e.g. Mg/Ca on planktonic foraminifera shells, relative abundance of planktonic foraminifera index species, alkenone index UK’37, transfer functions applied to assemblages of planktonic foraminifera, dinocysts, diatoms, coccoliths, etc.) are generally also confronted to similar discrepancies (e.g. Mazaud et al., 2002; Sicre et al., 2005; de Vernal et al., 2005, 2006; Peck et al., 2008; Penaud et al., 2011). To explain it, the authors usually call for differences in growth season and/or in depth habitat of the associated organisms, and/or for interannual variability, and/or for allochthonous advection. In the case of dinocyst-derived versus planktonic foraminifera-derived temperature reconstructions, many studies have mainly attributed these discrepancies to changes in depth habitat (e.g. de Vernal et al., 2005, 2006; Penaud et al., 2011). In our case, such an explanation is strongly coherent from an ecological point of view, given that: 1) While dinoflagellates, as part of the phytoplankton, are restricted to the photic layer (Sarjeant, 1974), heterotrophic planktonic foraminifera may live deeper (e.g. Schiebel et al., 2001). This is particularly true for the main species composing our foraminiferal assemblages since they do not bear any symbiont. 2) Our dinocyst-derived SSS (sea-surface salinity) records indicate the presence of a low saline surface layer throughout the last glacial period (mean of 31 and 32 psu for summer and winter SSS respectively). However, the planktonic foraminifera species identified in our assemblages (Table S1) barely tolerate such salinities (Tolderlund and Bé, 1971). Hence, given the ecological tolerances of the identified planktonic foraminifera species, it seems consistent to relate planktonic foraminifera assemblages to a depth habitat deeper than the one of dinocysts. However, as SST in the modern planktonic foraminifera database are extracted at 10 m water depth, it is a priori incoherent to interpret the reconstructed F-Temp as subsurface temperatures. Nonetheless, according to previous works focused on transfer functions (using the modern analog technique) applied to planktonic foraminifera assemblages, it seems reasonable to interpret the F-Temp signals as relative variations of subsurface temperatures in our study area. Indeed, for transfer functions sensu lato, the reference living-depth of foraminifera to consider in modern SST training sets is really problematic and its definition not trivial. Numerous tests were previously done on this question. Among them, Pflaumann et al. (1996) have demonstrated that such a consideration does not provide significant differences in the reconstructed F-Temp. Telford et al.
(2013) showed that “For cores north of 25°N, the [paleo]reconstructions from different depths and seasons resemble one another, with an offset”, implying that even if we have chosen another extraction depth for SST, the relative variations of our signals would be very similar. Furthermore, even if Telford et al. (2013) evidenced that for sites in the North Atlantic drift (including the nearby site NA87-22; cf. page 862) paleoreconstructions at all depth are statistically significant, he also argue that “the most ecologically relevant depth varies in space and time, and the assemblages will probably integrate the communities from several depths and seasons, so selecting a more appropriate fixed depth for temperature reconstructions for each location is probably not trivial and does not completely circumvent the problem.”. This latter statement is also supported by Adloff et al. (2011): “The currently used technique to reconstruct temperature from planktonic foraminifera [by extracting SST averaged over a depth interval depending on the living depth of the foraminifera species identified] is likely inadequate for time periods when the vertical temperature gradient was different from today”. Hence, it appears that there is no valuable reason to define a depth or a depth section (for the extraction of SST in the modern database) as more appropriate than another one, particularly because it must have evolved through time. Therefore, in our study area, it seems coherent to interpret the F-Temp signals – reconstructed from modern SST extracted at 10 m water depth – as relative variations of “subsurface” temperatures. The “subsurface” depth range is however difficult to define, but we can reasonably suppose that F-Temp signals are integrated over the potential depth range of the whole assemblage (i.e. 0-300 meters water depth here). Such an assumption allows for the conciliation of our phytoplanktonic-derived versus zooplanktonicderived signals, i.e. the reconstructed hydrological parameters as well as the environmental information carried by the respective assemblages (characterized by communities which ecologically do not sound as belonging to a common environment / water mass). Thus, it allows us to provide a constructive view of what can be interpreted from the strong difference calculated.
58 58 42 41 38 30 38 21 28 38 23 53 27 16 21 13 7 11 3 12 5 5 6 15 24 16 23 29 18 34
8 2 7 7 8 10 1 2 3 2 4 3 1 2 4 1
24 32 23 19 33 30 32 37 37 23 20 22 28 11 10 4 1 1 4 2 1 7 15 52 41 41 51 31 26
5 3 6 7 4 2 2 5 2 7 8 12 7
1 1
3 2
1 2
3
1 2 1
2
1
1 1 1
1 1
1 1 1
1
3 1 2 2
1 1 1
2 1
1
Total
Undetermined
H. adamsi
G. anfracta
G. uvula
G. conglomerata
O. bilobata
O. suturalis
Praeorbulina
G. theyeri
G. parkerae
T. hexagona
C. nitida
S. dehiscens
G. tumida
P. obliquiloculata
G. menardii
N. dutertrei
G. sacculiferus
G. trilobus
G. digitata
H. pelagica
G. crassaformis
G. calida
G. tenellus
G. conglobatus
G. ruber rosea
G. ruber alba
G. rubescens
T. humilis
O. universa
G. truncatulinoides senestre
G. truncatulinoides dextre
G. hirsuta
G. falconensis
H. aequilateralis
G. inflata
66 100 62 84 69 82 67 74 73 71 98 100 86 94 73 100 84 77 65 59 56 55 57 64 64 97 30 43 52 41 20 22 11 2 5 1 10 8 8 10 10 4 8 8 18 20 7 27 7 12 6 19 14 32 2 32 7 17 12 18
G. glutinata
N. incompta
107 116 125 143 122 85 112 129 136 154 185 171 151 254 245 314 341 342 334 348 350 355 319 286 261 276 261 260 288 295
G. scitula
N. pachyderma
12155 12179 12204 12228 12253 12277 12302 12326 12351 12375 12400 12866 13332 13799 14265 14731 15198 15664 16130 16597 17063 17529 17610 17690 17771 17851 17932 18012 18092 18140
G. quinquloba
Age (ka cal BP) - age model from Zumaque et al., 20102
300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590
G. bulloides
Depth (cm)
Table S1: raw planktonic foraminifera counts
2 371 362 1 360 1 361 2 355 2 357 2 367 1 373 1 371 1 351 1 352 1 384 2 378 2 360 375 375 363 359 357 1 383 1 372 377 373 351 4 360 360 373 374 1 362 385
6 5 6 6 7
1
1
5 3
45 49 40 50 43 37 33 36 31 37 42 52 40 45 40 42 43 59 30 22 45 47 51 43 36 39 50 39 54 36 44 81 19 23 16 2 1 3 9 3
1 1
1 1 2 1 1 2 2 2 1
2 2 1
1 3 1
1
1
1 1
Total
Undetermined
H. adamsi
G. anfracta
G. uvula
G. conglomerata
O. bilobata
O. suturalis
Praeorbulina
G. theyeri
G. parkerae
T. hexagona
C. nitida
S. dehiscens
G. tumida
P. obliquiloculata
G. menardii
N. dutertrei
G. sacculiferus
G. trilobus
G. digitata
H. pelagica
G. crassaformis
G. calida
G. tenellus
G. conglobatus
G. ruber rosea
G. ruber alba
G. rubescens
T. humilis
O. universa
G. truncatulinoides senestre
G. truncatulinoides dextre
G. hirsuta
G. falconensis
H. aequilateralis
G. inflata
35 14 23 8 26 11 33 7 23 41 20 25 16 21 16 19 15 10 20 27 19 16 24 32 31 24 29 19 36 17 15 10 30 26 37 39 12 17 24 27 26 33 22 40 30 38 24 19 14 24 15 19 25 21 20 16 22 30 39 20 19 32 53 25 24 9 23 12 14 15 6 20 4 58 3 17 19 53 38 101
G. glutinata
8 6 14 8 4 5 5 7 6 6 6 2 8 12 13 4 11 5 8 6 5 4 7 5 6 6 11 3 3 4 8 11 5
G. scitula
G. quinquloba
N. pachyderma
256 265 305 261 280 287 317 304 299 290 291 297 257 348 260 281 249 222 319 277 239 239 237 262 274 275 265 278 306 315 305 365 308 307 302 367 342 352 293 222
G. bulloides
Age (ka cal BP) - age model from Zumaque et al., 20102
18188 18236 18284 18332 18380 18427 18612 18797 18982 19167 19351 19536 19721 19906 20091 20275 20460 20645 20830 20984 21138 21292 21446 21600 21754 21908 22062 22217 22371 22525 22679 22833 22987 23141 23295 23449 23603 23757 23911 24066
N. incompta
Depth (cm)
600 610 620 630 640 650 660 670 680 690 700 710 720 730 740 750 760 770 780 790 800 810 820 830 840 850 860 870 880 890 900 910 920 930 940 950 960 970 980 990
358 351 397 359 392 374 392 383 362 382 375 408 361 453 368 352 361 362 388 356 350 352 363 353 356 356 373 356 415 415 408 538 365 366 353 395 411 381 386 376
3 4 7 9
3 12 9
1
2
2 1 2 5 1 2 1 1 1 4
3 1 2
2 2 5 21 18 5
3 1 7 13 13 14
2 6 19 21 18 7 1
7 21 29 31 29 29 18 6 20 51 68
1
1 1 2 1 1
1 4 1 1
1 3
1
1 2 1 1 2
Total
Undetermined
H. adamsi
G. anfracta
G. uvula
G. conglomerata
O. bilobata
O. suturalis
Praeorbulina
G. theyeri
G. parkerae
T. hexagona
C. nitida
S. dehiscens
G. tumida
P. obliquiloculata
G. menardii
N. dutertrei
G. sacculiferus
G. trilobus
G. digitata
H. pelagica
G. crassaformis
G. calida
G. tenellus
G. conglobatus
G. ruber rosea
G. ruber alba
G. rubescens
T. humilis
O. universa
G. truncatulinoides senestre
G. truncatulinoides dextre
G. hirsuta
G. falconensis
H. aequilateralis
G. inflata
G. glutinata
N. incompta
5 4 32 4 0 37 4 7 69 13 96 72 22 161 63 7 1 21 8 10 15 5 2 25 3 2 14 4 3 33 3 30 4 5 23 1 8 2 1 20 3 29 6 4 47 3 2 47 4 4 37 6 3 19 4 2 17 7 6 38 2 10 69 1 10 41 5 5 25 4 15 43 16 79 98 22 70 117 15 59 79 14 10 21 7 15 20 11 97 90 34 95 113 25 95 102 41 106 63 23 102 58 11 44 24 8 6 15 7 30 10 7 28 32 4 23 38
G. scitula
N. pachyderma
309 320 308 152 117 330 355 337 364 346 321 359 348 395 375 308 302 307 360 367 311 285 304 323 276 131 157 180 325 313 141 94 85 109 174 269 347 286 240 231
G. quinquloba
Age (ka cal BP) - age model from Zumaque et al., 20102
24220 24374 24528 24682 24836 24990 25144 25298 25452 25606 25760 25914 26069 26223 26377 26531 26685 26839 26993 27066 27139 27212 27284 27357 27430 27516 27601 27687 27992 28271 28550 28605 28659 28714 28768 28823 29037 29410 29784 30158
G. bulloides
Depth (cm)
1000 1010 1020 1030 1040 1050 1060 1070 1080 1090 1100 1110 1120 1130 1140 1150 1160 1170 1180 1190 1200 1210 1220 1230 1240 1250 1260 1270 1280 1290 1300 1310 1320 1330 1340 1350 1360 1370 1380 1390
355 362 397 357 382 361 389 370 383 390 354 395 357 421 407 366 357 352 388 390 363 367 363 361 352 363 398 353 370 364 367 387 359 367 396 368 382 354 358 366
4
1
2 7 4 2 6 1
4 8 11 6 8 2
2 1 6 2 5 2 2
1 1 3 2
15 38 5 3 2 1 1 13 13 16 13 8 7 6 10 23 27 16 43 29 28 10 15 27 55 53 32 28 20 15 18 2 1 9 30 43 14 8 9
1 1 1 4 1
1
1 2 3 2 1 2
2 1 1 1 1 1
1
6 1 3 5 1 2 4 2 1 2 1
1 3
1
Total
Undetermined
H. adamsi
G. anfracta
G. uvula
G. conglomerata
O. bilobata
O. suturalis
Praeorbulina
G. theyeri
G. parkerae
T. hexagona
C. nitida
S. dehiscens
G. tumida
P. obliquiloculata
G. menardii
N. dutertrei
G. sacculiferus
G. trilobus
G. digitata
H. pelagica
G. crassaformis
G. calida
G. tenellus
G. conglobatus
G. ruber rosea
G. ruber alba
G. rubescens
T. humilis
O. universa
G. truncatulinoides senestre
G. truncatulinoides dextre
G. hirsuta
G. falconensis
H. aequilateralis
G. bulloides
70 86 40 18 4 13 16 26 10 25 14 14 26 55 71 100 101 130 90 107 126 64 62 43 31 19 8 7 18 16 21 38 85 76 116 78 175 49 89 48 87 18 41 12 8 3 28 18 39 25 65 49 70 51 69 51 93 53 131 48 83 42 44 23 10 7 6 5 19 14 26 25 46 56 20 26 31 36 69 50
G. inflata
N. incompta
7 4 3 11 4 5 4 11 5 7 6 7 5 5 4 7 17 13 13 13 5 5 3 4 6 11 9 13 18 12 9 9 6 15 5 5 7 4 5 6
G. glutinata
N. pachyderma
209 285 330 306 317 343 291 181 111 145 137 272 321 351 332 302 194 166 132 185 217 293 337 296 267 177 188 217 173 164 237 290 351 344 359 293 197 293 276 255
G. scitula
Age (ka cal BP) - age model from Zumaque et al., 20102
30531 30905 31278 31652 31718 31784 31851 31917 32002 32106 32210 32315 32419 32685 33021 33304 33374 33444 33515 33585 33655 33806 34037 34268 34499 34730 34845 34960 35074 35189 35304 35419 35663 35922 36181 36440 36634 36762 36890 37018
G. quinquloba
Depth (cm)
1400 1410 1420 1430 1440 1450 1460 1470 1480 1490 1500 1510 1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 1620 1630 1640 1650 1660 1670 1680 1690 1700 1710 1720 1730 1740 1750 1760 1770 1780 1790
392 386 356 366 359 378 377 379 369 372 351 399 386 371 376 384 404 412 392 387 359 385 362 364 369 360 374 392 369 381 390 388 376 371 406 381 353 357 359 392
4 16 24 25 18 24 15 11 1
26 13 25 15 16 23 8 8 4 2 4
2 7 7
1 2 5 3 6 5 3 1
14 10 4 7 1 2 6 3 15 26 27 24 47 25 51
1 1
Total
Undetermined
H. adamsi
G. anfracta
G. uvula
G. conglomerata
O. bilobata
O. suturalis
Praeorbulina
G. theyeri
G. parkerae
T. hexagona
C. nitida
S. dehiscens
G. tumida
P. obliquiloculata
G. menardii
N. dutertrei
G. sacculiferus
G. trilobus
G. digitata
H. pelagica
G. crassaformis
G. calida
G. tenellus
G. conglobatus
G. ruber rosea
G. ruber alba
G. rubescens
T. humilis
O. universa
G. truncatulinoides senestre
G. truncatulinoides dextre
G. hirsuta
G. falconensis
H. aequilateralis
G. bulloides
70 83 79 91 96 123 94 110 82 70 84 59 73 38 53 15 16 8 6 5 4 5 7 4 10 21 27 114 54 127 53 42 46 20 9 22 12 11 5 14 16 15 23 23 17 32 42 107 21 75 119 76 71 71 58 105 43 83 49
G. inflata
N. incompta 18 22 36 15 16 12 9 19 5 3 5 3 3 6 8 6 2 3 4 6 5 4 5 4 10 17 8 13 14 16
G. glutinata
N. pachyderma 170 168 92 157 151 175 259 270 330 371 350 362 382 298 184 224 295 312 318 373 328 327 324 292 203 154 184 163 194 214
G. scitula
Age (ka cal BP) - age model from Zumaque et al., 20102 37146 37274 37402 37530 37658 37786 37914 38042 38170 38498 38826 39154 39482 39810 39910 40010 40110 40196 40281 40367 40453 40539 40624 40710 40827 40943 41060 41177 41293 41410
G. quinquloba
Depth (cm) 1800 1810 1820 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090
371 1 391 396 417 2 355 1 378 402 376 1 365 387 359 381 1 400 354 381 427 389 351 356 396 366 375 374 1 386 1 373 395 369 2 359 384 414
References:
Adloff, F., Mikolajewicz, U., Kučera, M., Grimm, R., Maier-Reimer, E., Schmiedl, G., and Emeis, K. C.: Upper ocean climate of the Eastern Mediterranean Sea during the Holocene Insolation Maximum A model study, Climate of the Past, 7, 1103-1122, 2011. de Vernal, A., Eynaud, F., Henry, M., Hillaire-Marcel, C., Londeix, L., Mangin, S., Matthiessen, J., Marret, F., Radi, T., Rochon, A., Solignac, S., and Turon, J. L.: Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the Last Glacial Maximum (LGM) based on dinoflagellate cyst assemblages, Quaternary Science Reviews, 24, 897-924, 2005. de Vernal, A., Rosell-Melé, A., Kucera, M., Hillaire-Marcel, C., Eynaud, F., Weinelt, M., Dokken, T., and Kageyama, M.: Comparing proxies for the reconstruction of LGM sea-surface conditions in the northern North Atlantic, Quaternary Science Reviews, 25, 2820-2834, 2006. Mazaud, A., Sicre, M. A., Ezat, U., Pichon, J. J., Duprat, J., Laj, C., Kissel, C., Beaufort, L., Michel, E., and Turon, J. L.: Geomagnetic-assisted stratigraphy and sea surface temperature changes in core MD94-103 (Southern Indian Ocean): Possible implications for North-South climatic relationships around H4, Earth and Planetary Science Letters, 201, 159-170, 2002. Peck, V. L., Hall, I. R., Zahn, R., and Elderfield, H.: Millennial-scale surface and subsurface paleothermometry from the northeast Atlantic, 55-8 ka BP, Paleoceanography, 23, PA3221 , doi:10.1029/2008PA001631, 2008. Penaud, A., Eynaud, F., Voelker, A., Kageyama, M., Marret, F., Turon, J. L., Blamart, D., Mulder, T., and Rossignol, L.: Assessment of sea surface temperature changes in the Gulf of Cadiz during the last 30 ka: Implications for glacial changes in the regional hydrography, Biogeosciences, 8, 2295-2316, 2011. Pflaumann, U., Duprat, J., Pujol, C., and Labeyrie, L. D.: SIMMAX: A modern analog technique to deduce Atlantic sea surface temperatures from planktonic foraminifera in deep-sea sediments, Paleoceanography, 11, 15-35, 1996. Sarjeant, W. A. S.: Fossil and living dinoflagellates, Elsevier, London, UK, 2013. Schiebel, R., Waniek, J., Bork, M., and Hemleben, C.: Planktic foraminiferal production stimulated by chlorophyll redistribution and entrainment of nutrients, Deep-Sea Research Part I: Oceanographic Research Papers, 48, 721-740, 2001. Sicre, M. A., Labeyrie, L., Ezat, U., Duprat, J., Turon, J. L., Schmidt, S., Michel, E., and Mazaud, A.: Mid-latitude Southern Indian Ocean response to Northern Hemisphere Heinrich events, Earth and Planetary Science Letters, 240, 724-731, 2005. Telford, R. J., Li, C., and Kucera, M.: Mismatch between the depth habitat of planktonic foraminifera and the calibration depth of SST transfer functions may bias reconstructions, Climate of the Past, 9, 859-870, 2013. Tolderlund, D. S. and Bé, A. W. H.: Seasonal Distribution of Planktonic Foraminifera in the Western North Atlantic, Micropaleontology, 17, 297-329, 1971.
