Guilderson, Thomas P. ; Caldeira, Kenneth ; Duffy, Philip B. 2000 Radiocarbon as a diagnostic tracer in ocean and carbon cycle modeling Global Biogeochem. Cycles Vol. 14 , No. 3 , p. 887 (1999GB001192) APPENDIX 1 - GEOSECS vs. Model comparison 14C Column inventories and penetration depth. Model description: Ocean model results are from the Lawrence Livermore National Laboratory's enhanced variant of the Geophysical Fluid Dynamics Laboratory Modular Ocean Model [Pacanowski et al., 1991]. In the runs presented here, the model was configured with 23 layers in the vertical, 7 of which were in the upper 300 m. The model includes the equation of state as well as equations for momentum, continuity, and tracer transport. Convection is represented by an adjustment scheme which mixes vertically adjacent grid cells when the potential density of the overlying cell exceeds that of the underlying one. The model has lightly smoothed bathymetry at a resolution of 2° latitude x 4° longitude. It represents flow through all major straits except for the Strait of Gibraltar, which is accounted for with a source of salt at the appropriate depth horizon. The simulations presented here include the "Gent-McWilliams" eddy parameterization [Gent and McWilliams, 1990]. Coefficients of vertical diffusivity are prescribed and depend on depth. Diffusivities increase from 0.2 cm2-sec-1 at the ocean surface to 1.3 cm2-sec-1 at the ocean bottom. In addition to treating the physical ocean circulation, the model also calculates concentrations and fluxes of the individual carbon isotopes. The model contains a simple "Redfield" biology model [Najjar et al., 1992] or more appropriately a biological chemical flux model with phosphate as the limiting nutrient. Fixation of silica by opal producers (diatoms) is allowed to outcompete calcium carbonate fixation (coccolithophorids), and as a consequence, the organic carbon to calcium carbonate rain ratio is not fixed a priori [e.g., Maier-Reimer, 1993]. Alkalinity is conserved and deep-sea carbonate dissolution occurs in waters that are undersaturated with respect to calcite or aragonite [Archer, 1991; Maier-Reimer, 1993]. Following the Ocean Carbon Model Intercomparison Project (OCMIP) standardization, gas exchange uses the Wanninkhof [1992] wind speed dependence and the solubility of Weiss [1974] and the model is forced with monthly climatological winds [Hellerman and Rosenstein, 1983]. This version of the model does not include an interactive sea-ice model. Instead, we used the climatological distribution of sea ice and sea ice inhibition of gas exchange [Zwally et al., 1983]. Surface salinities and temperatures are relaxed to the observed monthly climatology [Levitus and Boyer, 1994] with a time constant of 60 days. The model is spun-up in an accelerated mode; it was run for 3300 surface years with an acceleration factor of 7.5 (equivalent to ~25,000 years) in the deepest model level. We used a constant zero permil atmosphere and PCO2 of 280 µatm, to allow for deep ocean 14C equilibration. This seemingly long spin-up is necessary because waters outcropping in the Southern Ocean must be returned to the deep ocean prior to complete isotopic equilibration with the atmosphere. After being spun-up, the model was then run with evolving atmospheric PCO2 and D14C starting in 1765 as documented by archives and observational networks [Boden et al., 1993]. Similar to Toggweiler et al., [1989], three zonal atmospheric bands are used for the postbomb atmospheric forcing. ***** Appendix 1. GEOSECS and model comparison of the penetration and uptake of bomb-radiocarbon. For definitions see Broecker et al., Global Biogeochem. Cycles, 9, 263-288, 1995. Penetration depth in meters, DD amplitude is in per mil (”), and specific column inventory (CI: 10E9 atoms-cm-2) of bomb 14C. These are equivalent model grid-box station comparisons. GEOSECS MODEL Coll date Stn Lat (°N) Lon (°E) Basin PZ (m) DDamp CI PZ (m) DDamp CI 1972.6 3 51.0 -43.0 Atl 1692 63 17.6 641 145 14.6 1972.6 5 56.9 -42.6 Atl 1021 104 17.5 951 122 18.2 1972.6 11 63.5 -35.2 Atl 1134 90 16.9 1972.6 14 65.9 -27.5 Atl 501 143 10.6 1972.6 17 74.9 -1.1 Atl 837 102 14.1 3314 39 14.4 1972.7 18 70.0 0.0 Atl 961 122 19.4 901 102 12.7 1972.7 19 64.2 5.6 Atl 848 102 14.3 487 192 14.9 1972.7 23 60.4 -18.6 Atl 949 103 16.1 525 135 11.3 1972.7 27 42.0 -42.0 Atl 858 171 23.4 345 169 8.2 1972.7 29 36.0 -47.0 Atl 820 195 25.2 292 221 9.8 1972.7 31 27.0 -53.5 Atl 482 230 17.6 287 231 10.2 1972.7 33 21.0 -54.0 Atl 344 215 12 296 224 9.9 1972.8 37 12.0 -51.0 Atl 210 192 6.6 272 171 7.1 1972.8 40 3.9 -38.5 Atl 184 176 5.2 184 158 4.5 1972.8 48 -4.0 -29.0 Atl 154 149 3.7 265 126 5.2 1972.8 49 -7.9 -28.2 Atl 186 155 4.7 266 127 5.2 1972.9 54 -15.1 -29.5 Atl 284 162 7.4 362 143 7.9 1972.9 56 -21.0 -33.0 Atl 339 179 9.6 335 189 9.3 1972.9 58 -27.0 -37.0 Atl 353 189 10.5 273 220 9.0 1972.9 60 -33.0 -42.5 Atl 461 174 12.7 262 185 7.5 1972.9 64 -39.1 -48.6 Atl 329 151 7.9 570 196 17.9 1972.9 67 -45.0 -51.1 Atl 422 150 10.1 409 144 9.7 1973.0 68 -48.7 -46.0 Atl 416 115 8 354 142 8.4 1973.0 73 -53.0 -49.5 Atl 526 109 9.5 1973.0 74 -55.0 -50.1 Atl 248 89 3.7 593 109 10.7 1973.0 76 -57.7 -66.1 Atl 351 94 5.4 628 128 13.3 1973.0 78 -61.1 -63.0 Atl 203 81 2.8 400 119 8.1 1973.0 82 -56.3 -24.9 Atl 244 52 2.1 467 102 8.1 1973.1 89 -60.0 0.0 Atl 167 82 2.3 864 72 8.6 1973.1 90 -56.4 4.5 Atl 600 90 8.3 1973.1 91 -49.6 11.5 Atl 290 89 4.2 386 144 9.2 1973.1 92 -46.2 14.6 Atl 360 173 10.2 1973.1 93 -41.8 18.5 Atl 423 158 10.6 401 204 13.1 1973.1 94 -38.3 19.4 Atl 347 241 13.0 1973.1 103 -24.0 8.5 Atl 401 115 7.4 229 164 6.1 1973.1 107 -12.0 2.0 Atl 138 111 2.6 167 84 2.2 1973.2 111 2.0 -14.0 Atl 150 130 3.2 199 110 3.3 1973.2 113 11.0 -20.5 Atl 81 142 1.9 146 150 3.5 1973.2 115 28.0 -26.0 Atl 487 167 13 285 219 9.6 1973.2 117 30.7 -39.0 Atl 656 180 18.8 290 206 9.3 1973.2 120 33.3 56.6 Atl 778 171 21 1973.7 201 34.2 -123.9 Pac 232 239 8.9 156 183 4.8 1973.7 202 33.1 -139.6 Pac 278 256 11.1 262 262 10.4 1973.7 204 31.4 -150.0 Pac 280 228 9.9 268 239 9.4 1973.7 212 30.0 -159.8 Pac 270 239 9.4 1973.7 213 31.0 -168.5 Pac 308 237 11.1 292 211 9.0 1973.7 214 32.0 -177.0 Pac 402 195 11.9 313 198 9.1 1973.8 217 44.6 -176.8 Pac 338 156 8.4 309 156 7.3 1973.8 218 50.4 -176.6 Pac 283 149 7.1 155 215 5.5 1973.8 219 53.1 -177.3 Pac 372 116 7.4 147 201 4.8 1973.8 222 40.2 160.5 Pac 309 156 7.8 253 186 6.7 1973.8 223 35.0 151.8 Pac 503 213 16.3 301 219 9.6 1973.8 224 34.3 142.0 Pac 582 182 15.8 308 229 10.1 1973.9 225 32.6 161.9 Pac 490 200 14.9 316 216 9.9 1973.9 226 30.6 170.6 Pac 372 210 11.8 316 216 9.9 1973.9 227 25.0 170.1 Pac 337 235 12 314 232 10.5 1973.9 229 12.9 173.5 Pac 303 183 8.4 392 143 8.1 1973.9 231 14.1 -178.6 Pac 302 195 9.1 378 160 8.7 1973.9 235 16.8 -161.3 Pac 252 195 7.6 381 175 9.7 1974.0 239 5.9 -172.0 Pac 268 134 5.7 303 120 5.3 1974.0 241 4.6 179.0 Pac 257 137 5.7 262 119 4.6 1974.0 246 0.0 179.0 Pac 284 122 5.5 223 104 3.5 1974.0 251 -4.6 179.0 Pac 288 135 6.2 222 123 4.1 1974.0 257 -10.2 -170.0 Pac 323 152 7.7 276 142 5.8 1974.0 263 -16.7 -167.1 Pac 341 187 9.9 291 177 7.4 1974.1 269 -24.0 -174.5 Pac 456 174 12.3 312 223 10.0 1974.1 282 -57.5 169.8 Pac 365 116 6.9 515 131 11.2 1974.1 287 -69.3 -173.5 Pac 200 48 1.6 801 70 7.1 1974.2 290 -58.0 -174.0 Pac 346 87 5 406 180 12.2 1974.2 293 -52.6 -178.0 Pac 557 127 11.3 411 171 11.8 1974.2 296 -44.9 -166.7 Pac 427 143 9.7 553 173 15.0 1974.2 303 -38.4 -170.1 Pac 437 167 11.7 403 172 10.6 1974.2 306 -32.8 -163.6 Pac 316 192 9.4 276 220 8.8 1974.3 310 -27.0 -157.2 Pac 346 209 11.3 319 236 10.8 1974.3 317 -22.7 -127.2 Pac 384 191 11.4 330 204 9.7 1974.3 320 -33.3 -128.4 Pac 275 224 9.7 257 279 10.5 1974.3 322 -43.0 -129.9 Pac 394 172 10.8 442 185 12.9 1974.4 324 -23.0 -146.1 Pac 334 205 10.5 319 203 9.4 1974.4 326 -14.1 -126.3 Pac 517 95 7.7 361 127 7.3 1974.4 328 -9.3 -125.5 Pac 363 99 5.4 1974.4 331 -4.6 -125.1 Pac 242 91 3.6 280 100 4.2 1974.4 334 0.1 -124.6 Pac 171 123 3.4 221 86 2.9 1974.4 337 4.8 -124.1 Pac 177 111 3.2 246 104 4.2 1974.4 343 16.5 -123.0 Pac 174 180 5.1 213 182 5.6 1974.4 347 28.5 -121.5 Pac 244 175 222 6.3 1978.0 409 12.2 44.0 Ind 117 1978.0 413 13.4 53.3 Ind 311 137 7.1 1978.0 416 19.8 64.6 Ind 292 127 6.2 221 135 4.7 1978.0 417 13.0 64.5 Ind 213 140 5 208 123 3.9 1978.0 418 6.2 64.4 Ind 270 137 6 212 107 3.5 1978.0 419 4.0 56.8 Ind 215 156 5.4 228 110 3.8 1978.0 420 -0.1 50.9 Ind 221 152 5.4 260 110 4.3 1978.0 421 -6.2 50.9 Ind 182 151 4.5 270 96 3.9 1978.0 424 -12.3 53.7 Ind 357 164 9.1 215 93 3.1 1978.1 426 -18.9 54.8 Ind 533 151 12.1 1978.1 427 -27.1 57.0 Ind 618 180 17.3 504 213 16.1 1978.1 428 -37.8 57.6 Ind 667 166 17.5 491 174 12.8 1978.1 429 -47.7 57.9 Ind 382 103 6.4 418 160 11.2 1978.1 430 -60.0 61.0 Ind 288 93 4.6 359 149 9.1 1978.1 431 -64.2 84.0 Ind 208 48 1.7 389 131 8.5 1978.1 432 -59.3 92.6 Ind 267 76 3.5 501 124 10.1 1978.1 433 -53.0 103.0 Ind 439 67 4.9 587 135 13.1 1978.1 435 -40.0 110.0 Ind 660 169 17.8 626 140 13.4 1978.2 436 -29.3 110.0 Ind 551 194 16.8 445 225 15.4 1978.2 437 -24.5 104.9 Ind 522 197 16.1 452 210 14.3 1978.2 438 -19.5 101.3 Ind 461 187 13.4 341 200 10.1 1978.2 439 -13.0 97.1 Ind 316 183 8.9 211 181 5.4 1978.2 440 -9.4 95.0 Ind 179 159 4.6 220 147 4.5 1978.2 441 -5.0 91.8 Ind 159 179 4.6 188 141 3.8 1978.2 442 -1.2 90.8 Ind 162 178 4.6 196 126 3.9 1978.2 444 0.6 88.6 Ind 194 121 4.0 1978.2 445 8.5 86.0 Ind 152 165 4.1 202 127 3.9 1978.2 446 12.5 84.5 Ind 181 181 5.2 165 141 3.6 1978.3 447 5.0 100.0 Ind 166 166 4.6 1978.3 448 0.0 80.1 Ind 192 172 5.3 218 119 4.1 1978.3 449 -5.0 80.0 Ind 169 171 4.7 205 131 4.0 1978.3 450 -10.0 80.0 Ind 208 183 6.1 225 132 4.5 1978.3 451 -15.0 80.0 Ind 427 179 11.9 315 157 7.4 1978.3 452 -20.1 80.0 Ind 612 174 16.4 512 167 12.9 1978.3 453 -23.0 74.0 Ind 556 191 16.6 541 178 14.4 1978.3 454 -27.0 67.1 Ind 621 185 17.9 504 204 15.3