Late Quaternary pipe-or wen-like paleokarst features are being exhumed and modified by modem coastal processes along the north-western and northern coasts of Puerto Rico. These features are cigar-shaped tubes dissolved into host rock, with depths up to 4 rn, and widths of -0.5 m. They can be so densely packed that much of the original deposit has been removed. Most contain evidence of a few millimeters thick calcrete lining, consisting of micrite laminae, and a zone of indurated rock up to several centimeters thick of micrite and microspar. Many pipes are filled with insoluble material similar in appearance to the insolubles of the host rock but more concentrated, and augmented by material which resembles terra-rossa, At one site the pipes have retained this primary fill material, now somewhat cemented.At the other site the primary fill material, probably sand rather than rerra-rossa, was completely removed, the pipes re-filled with marine debris and the whole complex cemented. Some pipes show more than one cycle of filling, emptying and re-filling, and some areas show more than one phase of pipe formation.The pipes formed in the vadose zone, in poorly lithified, coarse-grained, Late Quaternary sandy limestones, by dissolution and reprecipitation along focused flow paths in a climatic regime with rain and strong evaporation. They may have formed within a few thousand years of host rock emplacement.

[1] We used Sr/Ca and stable isotope data from well dated and preserved corals from the northeastern Caribbean to determine the seasonal environmental conditions for four continuous years during the Eemian, the last time the Earth was in a prolonged warm phase. We determined that the seasonal range in SST during the Eemian was 25°-30°C. This is $1-2°larger than at present and caused primarily by winter cooling and, only to a small degree, by summer warming. As climate modeling studies indicate, the bias towards colder winters can be explained by changes in low latitude insolation induced by altered orbital parameters, modulated by atmospheric CO 2 levels that were lower than today. Milankovitch forcing at higher latitudes was probably less important.

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