Hydroclimate influences on modern pollen rain of upland southeastern Amazonia

Abstract

For accurate interpretations of palaeopalynological data, it is important to understand the influence of the current vegetation composition and characteristics on the formation of the palynological assemblage recorded in artificial or natural pollen traps. Therefore, in this study, modern pollen rain was characterized using artificial pollen traps under different ecological conditions and climatic seasons in Trilha da Mata Lake, Carajás North Ridge, southeastern Amazonia. The collection of pollen rain data comprises the total period from September 2015 to August 2016. There were two periods of low rainfall (September to December 2015 and May to August 2016) and one period of high rainfall (January to April 2016). The first two periods were represented by a predominance of canga vegetation pollen relative to forest pollen. Under dry conditions, the associations among the taxa Aparisthmium/Alchornea, Myrcia and Bellucia dichotoma were considered important for forest ecosystems, while those among Pleroma, Hyptis parkeri, Borreria and Perama carajensis were considered important for canga ecosystems. Under wet conditions, the forests were well represented by Schefflera, Anthurium lindmanianum, Pseudopiptadenia suaveolens and Glycydendron, and the most represented canga vegetation in the pollen rain were Poaceae undif., Miconia, M. acutistipula var. ferrea and Psychotria. Aparisthmium/Alchornea and Poaceae undif. Aparisthmium/Alchornea was related to periods of low water availability, and Poaceae undif. was associated with marshy or flooded environments. Thus, an increase in the influx of Poaceae undif. pollen grains was determined by variations in the extension of flooded areas, indicating an increase in the amount of rainfall and not the opposite case. Thus, future studies on vegetation reconstruction must consider modern pollen assemblages to precisely determine paleoenvironmental and paleoclimate conditions during sediment deposition.

Lake sedimentary processes and vegetation changes over the last 45k cal abpin the uplands of south‐eastern Amazonia

“…Pollen data suggest that montane savanna expanded and secondarily forests formed. Aparisthmium and Alchornea were very well represented, but their occurrences have been associated with periods of low water availability (da Silva et al, 2020). Additionally, they are highly common on intermediate taxa of the vegetation succession (Costa et al, 2018), which supports the interpretation of a strongly oscillating climate affecting the floristic pattern of the studied area.…”

“…[Color figure can be viewed at wileyonlinelibrary.com] stages, where macrophytes are dominant in inactive/filled lakes. Inactive lakes are dominated by Alismataceae, Cyperaceae (Eleocharis and Cyperus), Ponteridaceae (Sagittaria), Lentibulariaceae (Utricularia), Poaceae (Axonopus and Rhytachne), Xyridaceae (Xyris) and Mayacaceae (Mayaca) (Guimarães et al, 2017;da Silva et al, 2020).…”

“…Most of the Zn LV-1 and LV-2 samples (Gp-3) showed a positive charge in relation to the nMDS1 axis; these samples formed a third group, where the AM_T sample (Guimarães et al, 2017) occupied an intermediate position between the Zn LV-1 and LV-2 sample groups and the R5 samples. On the negative axis, the samples were more dispersed in the sorting space as Zn LV-3 and LV-4 samples (Gp-2) with LTM_T (da Silva et al, 2020), and a subset of the Zn LV-2 samples were determined by a smaller number of pollen types that are characteristic of the canga vegetation. The Kruskal stress value was 0.1007861 when using three dimensions in the NMDS for three ordinations.…”

“…Considering the spatial and temporal dynamics of vegetation, an NMDS analysis that integrated pollen data of lake sediment cores and modern pollen rain from Amendoim Lake-AM_T (Guimarães et al, 2017) and Lagoa da Trilha da Mata-LTM_T (da Silva et al, 2020) revealed higher similarities between the LV and R5 samples and the AM_T samples (Fig. 10), which are expected because these lakes are on the same plateau (Serra do S11) of Carajás and no geomorphic barrier for taxon dispersal and migration across the S11 plateau is present, such as dense forest cover (Lanes et al, 2018).…”

“…The anomalously low sea surface temperature in the equatorial western Atlantic (Jaeschke et al, 2007) and the cooler climatic conditions, with an estimated temperature Figure 10. NMDS analysis of the distribution of the modern pollen rain from the Amendoim Lake -AM_T (Guimarães et al, 2017) and Lagoa da Trilha da Mata -LTM_T samples (da Silva et al, 2020) with the sediment core samples (R5, LV and ST02) according to zones of pollen and spore assemblages (palynozones). [Color figure can be viewed at wileyonlinelibrary.com] of 3°C, during the LGM for the Carajás region (Reis et al, 2017) may have suppressed the moisture supply from the ocean (Cook and Vizy, 2006), weakened the ITCZ and reduced the moisture convection (Koutavas and Joanides, 2012).…”