Figure 1.
Map satellite image and photograph of the Diablas coastal lagoon.
(A) Map of the Galápagos Islands. Diablas lagoon is located in the Diablas wetlands on the south side of Isla Isabela. (B) Satellite image of the Diablas wetlands. The coring location is marked with a circle on both satellite images and the lagoon outline has been traced (Source: GoogleEarth © 2010). (C) View from the far-east side of Diablas lagoon, Isabela, looking NW.
Table 1.
AMS radiocarbon calibration results.
Figure 2.
Age-depth, organic and stratigraphic changes observed in the Diablas core.
Figure 3.
(A) C/N and δ13C results of surface samples of mangroves and microbial mats in Diablas; (B) Comparison between linear fitting (dashed line) and the logistic curve (full line) fitting methodology used in our model. (C) Stable isotope values and (D) mixing model output for Diablas lagoon.
Figure 4.
ICP-AES geochemical data from the Diablas lagoon core.
Geochemical variations in 18 rare earth elements from the core from the Diablas lagoon. The dashed-red line denotes the major sediment transition identified in figure 2. Blue-shaded area (2700−1990 cal yr BP) indicates the point at which S and associated elements increased, and may indicate increasing tidal influence at the site. Green-shaded area denotes the period (2100−1600 cal yr BP) when geochemical in-wash element indicators (Al, Ti and Fe) were found in higher concentrations in the lagoon and are thought to be indicative of tidal disturbances.
Figure 5.
Reconstruction of ecological changes and environmental changes at Diablas lagoon for the past 2,700 years.
Note that for the RSL data, seven different modelling parameters are provided (see methods section). The medium parameter model is marked by the thick-blue line. Grain size data is from El Junco crater-lake, San Cristobal (see ref. 19).
Figure 6.
Hypothesised model of environmental changes inferred at Diablas lagoon over the Holocene.
Figure 7.
Threshold ecological response at Diablas lagoon.
A) Stable isotope mixing model results indicating the main ecological changes at the Diablas lagoon. B) Phase plot to indicate the presence of alternative stable states (mangroves and microbial mat) in the lagoon system. The point at which the threshold between the two states was crossed is marked by a red dashed line. Detailed chronological summary is as follows. (i) 2770 cal yr BP- resilient mangrove stand at the coring site; (ii) 2000 cal yr BP- increase in sediment accumulation rates denotes feedback response of resilient mangroves in response to environmental disturbances; (iii) 1400 cal yr BP- opening of the mangrove canopy due to preceding tidal disturbance events, eroding resilience over time; (iv) (940 cal yr BP) Drier background climatic conditions and slightly decreasing RSL combine, resulting in threshold transition to microbial mat; (v) present day; contemporary lagoon conditions with cyanobacterial mat at the sediment surface.