CONICET | Buscador de Institutos y Recursos Humanos

In paleoclimatology, the concept of latitudinal insolation gradients (LIGs), reckoned in various ways, has received increasing attention regarding glacial/inter-glacial climatic transitions and oscillations. In particular, the Holocene, which permits the reconstruction of past climatic proxies with an increasingly finer spatial and temporal resolutions, has provided evidence that suggests that LIGs are a key forcing on climate at different timescales. Nevertheless, LIGs´ own dynamics (chiefly their variations in relation to astronomical parameters and geographical zones) and even basic definitions, have not been properly investigated, especially during the last part of the present geological epoch. The main reason is the lack of broadly accessible, theoretical insolation data that account for short-term orbital variations (i.e., for describing sub-Milanković-orbital forcing during the Holocene). Based on our latest astronomical-orbital solutions, we present an in-depth discussion on the calculation of LIGs and their variations all through the Holocene and 1 kyr into the future. Our results show a much more complex variety and behaviour of LIGs than those that were shown previously. We report that during the studied period, daily LIGs in summer, around the solstitial days (both hemispheres), are strongly modulated by obliquity only at mid-latitude band, whereas at tropical and polar bands LIGs are modulated by precession. Summer half-year LIGs for the Northern Hemisphere show a marked modulation in out-of-phase sense with obliquity, just for the mid-latitude and polar bands. Surprisingly, this competing effect between precession and obliquity also produces the fact that the southern counterpart of these LIGs are more modulated by precession than obliquity. In cases involving inter-band latitudes or different intra-annual lapses, they need to be examined separately and carefully and the results could be very different from traditional presumptions. Our novel results and study are based on the precise estimation of the duration of the orbital interval considered in the definition of LIGs. Our new study also avoids the difficulties of insolation calculations regarding the relationship between orbital longitudes and time.

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