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Umbric ferralsols (UF) have organic carbon stocks within the first 1 m of soil profile depth that are nearly double the size (~19 kg C m−2) compared to the average carbon stocks of all other ferralsols (~10 kg C m−2). Here, we investigate processes that allow UF to gain and maintain such extraordinary carbon stocks. Using the International Soil Research and Information Center database, complemented with recently published datasets, we show that the carbon saturation capacity of the clay + silt fractions in UF (22.8 ± 5.7 g C kg−1 soil, n = 59) does not exceed the carbon saturation capacity in other ferralsols (23.3 ± 6.2 g C kg−1 soil, n = 165), thus eliminating a particularly retentive mineral matrix as a possible explanation. Rather, carbon stocks were correlated with the thickness of A horizons (106 ± 49 cm, n = 59 in umbric versus 35 ± 22 cm, n = 165 in non‐umbric ferralsols). We subsequently hypothesized that differences in A‐horizon thickness arose from two pedogenic scenarios: (i) superior carbon accrual resulting from a unique vegetation cover capable of allocating large quantities of carbon to belowground plant organs; and (ii) geomorphic processes that led to carbon burial. We evaluated the plausibility of these scenarios considering landscape history and associated carbon flux rates, hillslope position, as well as δ13C values and Ti/Zr ratios for subsets of ferralsol profiles studied by us in a region that encompasses latitudes from 26 to 7°S in eastern Brazil. We found that exceptional carbon stocks were most prevalent in the gradual transition zone (ecotone) between savanna and rainforest, likely resulting from erosion–deposition processes, historic changes of vegetation cover composed of grasses and arboreal elements, and active bioturbation. We suggest that attempts to sequester carbon in non‐umbric ferralsols will be most successful if they emulate or promote the biotic and abiotic processes prevalent in the savanna/rainforest ecotone.

Abstract. Amongst the most devastating marine catastrophes that can occur in coastal areas, are storms and tsunamis, which may seriously endanger human society. Many such events are known and have been reported for the Mediterranean, a region where high-frequency occurrences of these extreme events coincides with some of the most densely populated coastal areas in the world. In a sediment core from Mar Menor Lagoon (SE Spain), we discovered eight coarse grained layers which document marine incursions during periods of intense storm activity or tsunami events. Based on radiocarbon dating, these extreme events occurred around 5250, 4000, 3600, 3010, 2300, 1350, 650 and 80 years cal B.P.. No comparable events have been observed during the 20th and 21th centuries. The results indicate little likehood of a tsunami origin for these coarse grained layers, although historical tsunami events are recorded in this region. These periods of surge events seem to coincide with the coldest periods in Europe during the late Holocene, suggesting a control by a climatic mechanism for periods of increased storm activity. Spectral analyses performed on the sand % revealed four major periodicities of 1228 ±327, 732 ±80, 562 ±58, and 319 ±16 yr. Amongst the well-known proxies that have revealed a millennial-scale climate variability during the Holocene, the ice-rafted debris (IRD) indices in North Atlantic developed by Bond et al. (1997, 2001) present a cyclicity of 1470 ±500 yr, which matches the 1228 ±327 yr periodicity evidenced in the Mar Menor lagoon, considering the respective uncertainties on the periodicities. Thus, an in-phase storm activity in Western Mediterranean is found with the coldest periods in Europe and to the North Atlantic thermohaline circulation. However, further investigations, such as additional coring, high-resolution coastal imagery, are needed to better constrain the main cause of these multiple-events.

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