José Ignacio Martínez

Mangrove dynamics in the southwestern Caribbean since the ‘Little Ice Age’: A history of human and natural disturbances

Relatively little is known about the long-term response of Caribbean mangroves to human and natural disturbances during the ‘Little Ice Age’ (LIA). We present new palynological information on the dynamics of the Bahia Honda mangrove from the eastern coast of San Andres Island in the southwestern Caribbean for the late Holocene. Major changes in the Bahia Honda pollen record show the combined effects of natural events (strong storms and sea-level rise), and human disturbances. These changes are supported by 14C dates, sedimentological and palynological information. A storm (most probably a hurricane) was recorded around AD 1600, caused sediment reworking and the subsequent loss of about 2000 years of the vegetation record. The devastation of tree vegetation by this event allowed the expansion of heliophytic vegetation (e.g. grasses and vines). Mangroves and coastal vegetation started to recover at AD 1700, reaching their maximum extent within a few decades, when microforaminifera shells became abundant at the coring site, thus suggesting a relative sea-level rise because of the geomorphic reconfiguration of the coastal plain after the storm. Furthermore, the pollen evidence indicates more humid regional climates during the late LIA (AD 1700—1850). Mangrove and coastal vegetation declined sharply as a consequence of the establishment of coconut plantations around AD 1850. The recovery of the mangroves after AD 1960 is a result of the combined effect of relative sea-level rise and drastic changes in the local economy from coconut plantations to commerce.

PALEOXIGENACIÓN Y PALEOPRODUCTIVIDAD EN EL GOLFO DE PANAMÁ DURANTE EL HOLOCENO TARDÍO

Paleocenographic conditions in the Panama Bight for the past 4000 years were inferred by using the micropaleontological record from the deep sea core KNR176-2-MC4 (7.27°N, 78.24°W; water depth 2121 m). The epifauna-infauna relationship of deep-sea benthic foraminifera and their diversity gradually increase up-core, which is interpreted as a result of: (1) a decrease in the dissolved oxygen content towards the recent and, (2) higher taphonomic effects which modify the original composition of the microfauna. Indicative taxa of moderate oxygen conditions, such as Uvigerina proboscidea and Oridorsalis umbonatus were found at the base of the core. In contrast, lower oxygenation and higher productivity conditions are inferred by the common presence of Globobulimina affinis and Uvigerina proboscidea. Additional paleoproductivity indicators such as Epistominella spp. and Uvigerina peregrina were more common in the middle part of the core. The comparison of the MC4 core micropaleontological record with several paleoclimatic records from the Panama isthmus (the Woodhouse Lake, and the Chilibrillo stalagmite) illustrates that a higher recurrence of El Niño events since 5000 years BP, could be related to a higher frequency and intensity of upwelling processes in the Panama Gulf. However, the magnetic susceptibility of the MC4 core presents variations which cannot be related with to a reduction in local rainfall.