# Lake Challa 25,000 Year BIT Index Data #----------------------------------------------------------------------- # World Data Service for Paleoclimatology, Boulder # and # NOAA Paleoclimatology Program #----------------------------------------------------------------------- # Template Version 4.0 # Encoding: UTF-8 # NOTE: Please cite original publication, NOAA Landing Page URL, dataset and publication DOIs (where available), # and date accessed when using these downloaded data. If there is no publication information, please cite investigator, study title, NOAA Landing Page URL, and date accessed. # # NOAA_Landing_Page: https://www.ncei.noaa.gov/access/paleo-search/study/13539 # Landing_Page_Description: NOAA Landing Page of this file's parent study, which includes all study metadata. # # Study_Level_JSON_Metadata: https://www.ncei.noaa.gov/pub/data/metadata/published/paleo/json/noaa-lake-13539.json # Study_Level_JSON_Description: JSON metadata of this file's parent study, which includes all study metadata. # # Data_Type: Paleolimnology # # Dataset_DOI: 10.25921/da6x-9z97 # # Science_Keywords: hydrology #-------------------- # Resource_Links # # Data_Download_Resource: https://www.ncei.noaa.gov/pub/data/paleo/paleolimnology/eastafrica/challa2009bit-noaa.txt # Data_Download_Description: NOAA Template File; Tetraether Data # # Original_Source_URL: # Original_Source_Description: # #-------------------- # Contribution_Date # Date: 2012-11-15 #-------------------- # File_Last_Modified_Date # Date: 2022-09-21 #-------------------- # Title # Study_Name: Lake Challa 25,000 Year BIT Index Data #-------------------- # Investigators # Investigators: Verschuren, D.(https://orcid.org/0000-0002-9116-5446); Sinninghe Damsté, J.S.(https://orcid.org/0000-0002-8683-1854); Moernaut, J.(https://orcid.org/0000-0003-3164-4274); Kristen, I.; Blaauw, M.(https://orcid.org/0000-0002-5680-1515); Fagot, M.; Haug, G.H.(https://orcid.org/0000-0001-7534-4420) #-------------------- # Description_Notes_and_Keywords # Description: The 172 main-series BIT samples (branched and isoprenoid tetraether index of soil bacterial versus aquatic archaeal membrane lipids) (cf. Fig.2 of the source publication) are 4-cm core increments extracted at constant 12-cm composite-depth intervals, plus 7 additional samples (samples at composite depths 118, 774, 958, 966, 970, 1050, 1074, and 2014 cm) filling in sharp transitions in BIT values (mainly around the Younger Dryas period) and 1 sample replacing the missing sample at 122 cm. The high-resolution BIT time series for the last millennium (cf. Supplementary Fig.7 of the source publication) adds 21 samples (highlighted in blue) from the uppermost 126 cm, to produce a contiguously sampled record of 4-cm core increments. The 3-pt running mean BIT values are based on main-series samples only. 'Composite depth' refers to the continuous depth axis of the master core sequence, which is composed of 21 cross-correlated core sections before excision of 5 turbidites. 'Corrected depth' refers to the depth axis of the master sequence after excision of these turbidites (they occur below samples at composite depths of 482, 674, 1898, 1910, and 2018 cm), and represents a continuous time axis. #-------------------- # Publication # Authors: Verschuren, D., J.S. Sinninghe Damste, J. Moernaut, I. Kristen, M. Blaauw, M. Fagot, G. H. Haug, and CHALLACEA project members # Journal_Name: Nature # Published_Title: Half-precessional dynamics of monsoon rainfall near the East African Equator # Published_Date_or_Year: 2009 # Volume: 462 # Pages: 637-641 # Issue: 7273 # Report_Number: # DOI: 10.1038/nature08520 # Full_Citation: # Abstract: External climate forcings - such as long-term changes in solar insolation - generate different climate responses in tropical and high latitude regions. Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-rich middle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few, especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (~11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions. #-------------------- # Funding_Agency # Funding_Agency_Name: European Science Foundation # Grant_Number: CHALLACEA project #-------------------- # Site_Information # Site_Name: Lake Challa # Location: Kenya # Northernmost_Latitude: -3.3167 # Southernmost_Latitude: -3.3167 # Easternmost_Longitude: 37.7 # Westernmost_Longitude: 37.7 # Elevation: 880 #-------------------- # Data_Collection # Collection_Name: Challa2009bit # First_Year: 24922 # Last_Year: -30 # Time_Unit: cal yr BP # Core_Length: 21.62 # Parameter_Keywords: geochemistry # Notes: Composite core #-------------------- # Chronology_Information # Chronology: # # #------------------ # Variables # # PaST_Thesaurus_Download_Resource: https://www.ncdc.noaa.gov/paleo/skos/past-thesaurus.rdf # PaST_Thesaurus_Download_Description: Paleoenvironmental Standard Terms (PaST) Thesaurus terms, definitions, and relationships in SKOS format. # # variables format: shortname what,material,error,units,seasonality,data_type,detail,method, C(har) or N(umeric) data,additional information # ## depth_cm depth,,,centimeter,,paleolimnology,,,N,composite depth ## depth_corrcm depth,,,centimeter,,paleolimnology,corrected,,N, ## age_calBP age,,,calendar year before present,,paleolimnology,,,N, ## age_AD age,,,year Common Era,,paleolimnology,,,N, ## BITindex branched and isoprenoid tetraether index,sediment,,,,paleolimnology,,,N, ## BITindex-3pt branched and isoprenoid tetraether index,sediment,,,,paleolimnology,smoothed,,N,3-point smoothed #-------------------- # Data: # Data lines follow (have no #) # Data line format - tab-delimited text, variable short name as header # Missing_Values: na depth_cm depth_corrcm age_calBP age_AD BITindex BITindex-3pt 2 2 -30 1980 0.68 0.63 6 6 8 1942 0.61 na 10 10 46 1904 0.63 na 14 14 83 1867 0.62 0.59 18 18 120 1830 0.60 na 22 22 156 1794 0.52 na 26 26 191 1759 0.48 0.58 30 30 225 1725 0.65 na 34 34 258 1692 0.60 na 38 38 290 1660 0.61 0.64 42 42 321 1629 0.72 na 46 46 351 1599 0.68 na 50 50 381 1569 0.73 0.65 54 54 409 1541 0.64 na 58 58 437 1513 0.56 na 62 62 465 1485 0.63 0.63 66 66 493 1457 0.60 na 70 70 521 1429 0.66 na 74 74 550 1400 0.61 0.61 78 78 579 1371 0.56 na 82 82 609 1341 0.60 na 86 86 641 1309 0.60 0.57 90 90 673 1277 0.55 na 94 94 707 1243 0.50 na 98 98 743 1207 0.56 0.56 102 102 780 1170 0.46 na 106 106 818 1132 0.66 na 110 110 858 1092 0.60 0.60 114 114 899 1051 0.61 na 118 118 941 1009 0.64 0.66 122 122 984 966 na na 126 126 1028 922 0.75 na 134 134 1118 832 0.79 0.69 146 146 1259 691 0.65 0.68 158 158 1404 546 0.60 0.64 170 170 1554 396 0.67 0.62 182 182 1709 241 0.58 0.61 194 194 1868 82 0.58 0.61 206 206 2031 na 0.67 0.65 218 218 2199 na 0.70 0.69 230 230 2370 na 0.72 0.70 242 242 2543 na 0.70 0.69 254 254 2713 na 0.66 0.65 266 266 2877 na 0.61 0.63 278 278 3032 na 0.63 0.61 290 290 3176 na 0.60 0.62 302 302 3313 na 0.61 0.62 314 314 3448 0.64 0.63 326 326 3586 0.65 0.66 338 338 3731 0.70 0.68 350 350 3888 0.68 0.69 362 362 4064 0.70 0.70 374 374 4261 0.71 0.69 386 386 4479 0.65 0.65 398 398 4708 0.59 0.60 410 410 4932 0.54 0.56 422 422 5134 0.55 0.54 434 434 5312 0.51 0.54 446 446 5473 0.55 0.54 458 458 5619 0.57 0.58 470 470 5756 0.64 0.59 482 482 5888 0.57 0.58 518 491 5987 0.53 0.53 530 503 6123 0.50 0.52 542 515 6265 0.52 0.55 554 527 6413 0.63 0.58 566 539 6566 0.58 0.59 578 551 6722 0.57 0.54 590 563 6882 0.46 0.52 602 575 7042 0.53 0.49 614 587 7204 0.47 0.50 638 611 7523 0.51 0.51 650 623 7679 0.54 0.53 662 635 7830 0.53 0.53 674 647 7978 0.52 0.55 722 662 8161 0.60 0.54 734 674 8313 0.50 0.56 746 686 8475 0.58 0.58 758 698 8655 0.66 0.63 770 710 8858 0.64 0.64 774 714 8932 0.61 0.69 782 722 9087 0.83 0.74 794 734 9336 0.79 0.82 806 746 9596 0.84 0.85 818 758 9851 0.91 0.91 830 770 10088 0.98 0.96 842 782 10299 0.99 0.97 854 794 10482 0.95 0.97 866 806 10641 0.97 0.96 878 818 10782 0.98 0.97 890 830 10908 0.98 0.97 902 842 11024 0.96 0.97 914 854 11135 0.97 0.95 926 866 11245 0.92 0.96 938 878 11360 0.98 0.94 950 890 11483 0.92 0.94 958 898 11572 0.90 0.86 962 902 11619 0.75 0.84 966 906 11667 0.87 0.76 970 910 11717 0.65 0.68 974 914 11768 0.53 0.56 986 926 11928 0.52 0.53 998 938 12097 0.55 0.50 1010 950 12271 0.42 0.46 1022 962 12447 0.40 0.39 1034 974 12625 0.35 0.36 1046 986 12801 0.33 0.36 1050 990 12858 0.40 0.46 1058 998 12972 0.64 0.55 1070 1010 13140 0.59 0.63 1074 1014 13195 0.66 0.68 1082 1022 13307 0.79 0.75 1094 1034 13476 0.79 0.74 1106 1046 13649 0.65 0.65 1118 1058 13826 0.53 0.59 1130 1070 14008 0.60 0.57 1142 1082 14196 0.57 0.55 1154 1094 14390 0.49 0.51 1166 1106 14589 0.48 0.48 1178 1118 14791 0.48 0.49 1190 1130 14995 0.49 0.47 1202 1142 15197 0.42 0.44 1214 1154 15396 0.40 0.42 1226 1166 15590 0.42 0.42 1238 1178 15776 0.42 0.39 1250 1190 15953 0.32 0.36 1262 1202 16116 0.34 0.35 1274 1214 16267 0.39 0.35 1286 1226 16407 0.34 0.35 1298 1238 16537 0.33 0.32 1310 1250 16660 0.29 0.31 1322 1262 16778 0.31 0.31 1334 1274 16891 0.32 0.31 1346 1286 17002 0.29 0.33 1358 1298 17112 0.37 0.31 1370 1310 17222 0.28 0.32 1382 1322 17332 0.32 0.30 1394 1334 17443 0.29 0.31 1406 1346 17554 0.33 0.31 1418 1358 17666 0.31 0.32 1430 1370 17778 0.31 0.31 1442 1382 17891 0.31 0.31 1454 1394 18005 0.31 0.31 1466 1406 18120 0.30 0.32 1478 1418 18235 0.33 0.32 1490 1430 18350 0.33 0.34 1502 1442 18465 0.35 0.32 1514 1454 18578 0.29 0.33 1526 1466 18690 0.34 0.31 1538 1478 18800 0.31 0.33 1550 1490 18907 0.34 0.32 1562 1502 19012 0.32 0.33 1574 1514 19116 0.32 0.31 1586 1526 19223 0.29 0.31 1598 1538 19336 0.33 0.31 1610 1550 19457 0.32 0.34 1622 1562 19588 0.36 0.33 1634 1574 19726 0.29 0.33 1646 1586 19865 0.34 0.32 1658 1598 20003 0.33 0.35 1670 1610 20134 0.40 0.35 1682 1622 20256 0.32 0.35 1694 1634 20363 0.33 0.36 1706 1646 20452 0.42 0.47 1718 1658 20523 0.67 0.51 1730 1670 20579 0.44 0.56 1742 1682 20626 0.57 0.50 1754 1694 20669 0.48 0.53 1766 1706 20712 0.54 0.51 1778 1718 20761 0.51 0.49 1790 1730 20821 0.42 0.47 1802 1742 20896 0.48 0.44 1814 1754 20990 0.41 0.42 1826 1766 21102 0.37 0.40 1838 1778 21229 0.42 0.45 1850 1790 21369 0.57 0.49 1862 1802 21520 0.48 0.51 1874 1814 21679 0.50 0.46 1886 1826 21845 0.40 0.42 1898 1838 22014 0.38 0.45 1910 1844 22100 0.57 0.62 1934 1861 22337 0.91 0.73 1946 1873 22498 0.70 0.80 1958 1885 22653 0.78 0.82 1970 1897 22802 0.99 0.91 1982 1909 22948 0.97 0.98 1994 1921 23089 0.97 0.92 2006 1933 23229 0.82 0.79 2014 1941 23321 0.58 0.61 2018 1945 23367 0.43 0.47 2042 1953 23458 0.40 0.58 2054 1965 23596 0.91 0.60 2066 1977 23734 0.48 0.73 2078 1989 23874 0.80 0.74 2090 2001 24015 0.93 0.79 2102 2013 24160 0.64 0.84 2114 2025 24308 0.96 0.80 2126 2037 24459 0.81 0.79 2138 2049 24611 0.59 0.78 2150 2061 24766 0.95 0.73 2162 2073 24922 0.65 0.80