The Milankovitch-Croll hypothesis states that glacial-interglacial climate change occurs in response to cyclic shifts in the geometry of Earth’s orbit. These cycles arise from changes in eccentricity, axial tilt, and the precession of the seasons. The cycles control solar insolation (solar energy received per unit time per unit area). The orbital cycles range from 20,000 to 400,000 years and are best known from the Plio-Pleistocene record. However, evidence of these cycles can be found in older sedimentary rocks. Longer solar insolation cycles that are unresolved by current paleoclimate records may also be present.
I’ve been fortunate to receive training from John Imbrie, Warren Prell, Alan Mix, and Nick Pisias, researchers who were instrumental in the development of our understanding of Milankovitch-scale climate change as part of the CLIMAP and SPECMAP projects.
I sailed on Ocean Drilling Program (ODP) Legs 162 – North Atlantic Arctic Gateways, and ODP Leg 177 – Southern Ocean Gateways. These expeditions explored the role of heat transport by the Atlantic Meridional Overturning Circulation on glacial interglacial timescales.
Publications:
A reconstruction of late Pleistocene relative sea level in the south Bohai Sea,China, based on sediment grain-size analysis, L Yi, H Yu, X Xu, JD Ortiz, C Deng, X Qiang and H Huang, Sedimentary Geology, (281), 88-100.
Late Quaternary linkage of sedimentaryrecords to three astronomical rhythms and the Asian monsoon, inferred from a coastal borehole in the south Bohai Sea, China, L Yi, H-J Yu, JD Ortiz, X-Y Xu, S-L Chen, J-Y Ge, Q-Z Hao, J Yao, X-F Shi and S-Z Peng, Palaeogeography,Palaeoclimatology, Palaeoecology, (329-330), 101-117.
Reflectance-based clay mineral cycles in Quaternary sediments from the Northwind Ridge: implications for glacial-interglacial sedimentation patterns in the Arctic Ocean, L Yurco, JD Ortiz, L Polyak and D Darby, Polar Research.
Microevolution and Speciation in Thalassiosira weissfloggi, U Sorhannus, JD Ortiz and M Wolf, Protist, (16), 237-249.
Sediment record from the western Arctic Ocean with an improved Late Quaternary age resolution: HOTRAX core HLY0503-8JPC, Mendeleev Ridge, RE Adler, L Polyak, JD Ortiz, DS Kaufman, JET Channell, C Xuan, AG Grottoli, E Sellen and KA Crawford, Global and Planetary Change, (68), 18-29.
Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean, L Polyak, J Bischof, JD Ortiz, DA Darby, JET Channell, C Xuan, DS Kaufman, R Løvlie, DA Schneider, DD Eberl, RE Adler, EA Council and Late, Global and Planetary Change, (68), 5-17.
Marine radiocarbon evidence for the mechanism of deglacial atmospheric CO2 rise, TM Marchitto, SJ Lehman, JD Ortiz, J Fluckinger and A van Geen, Science, 316 (5830), 1456.
Sediment Cd and Mo accumulation in the oxygen-minimum zone off western Baja California linked to global climate over the past 52 kyr, WE Dean, Y Zheng, JD Ortiz and A. van Geen, Paleoceanography, (21), PA4209.
Enhanced marine productivity off western North America during warm climate intervals of the past 52 kyr, JD Ortiz, S O’Connell, J DelViscio, W Dean, J Carriquiry, T Marchitto, Y Zheng and A. van Geen, Geology, 32(6), 521-524.
1999 RV Melville Baja California cruise, On the preservation of laminated sediments along the western margin of North America, A van Geen, Y Zheng, JM Bernhard, KG Cannariato, J Carriquiry, WE Dean, BW Eakins, JD Ortiz, J Pike and other participants, Paleoceanography, 18(4),1098.
Diffuse spectral reflectance as a proxy for percent carbonate content in North Atlantic sediments, JD Ortiz, A Mix, S Harris and S O’Connell, Paleoceanography, (14), 171-186.
Data report: Spectral reflectance observations from Leg 162 recovered sediments, JD Ortiz, S O’Connell, Leg 162 Shipboard Sedimentologists and A Mix, in Proceedings of the Ocean Drilling Program, Scientific Results, 162, ME Raymo, E Jansen, O Blum and TD Herbert (Eds.), College Station, TX, (Ocean Drilling Program), 259-264.
Low-frequency oscillations in Site 983 sediments: Relationships between carbonate and productivity proxies, S Hyun, JD Ortiz, ME Raymo and A Taira, Proceedings of the Ocean Drilling Program, Scientific Results, 162, in ME Raymo, E Jansen, P Blum and TD Herbert (Eds.), College Station, TX, (Ocean Drilling Program), 197-207.