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Climate changes and solar cycles recorded at the Holocene Paraná Delta, and their impact on human population.

Milana JP, Kröhling D - Sci Rep (2015)

Bottom Line: The evolution of this 17,400 km(2) delta enclosed in Plata estuary, can be tracked by a series of 343 successive coastal-ridges showing a c.11 years period, in coincidence with sunspot cycle, also found in some North Hemisphere coastal-ridge successions.Results suggest that aside the solar forcing, both short and medium term climate changes controlled delta evolution.An important learning is that a slight cooling would turn the highly productive pampas, into that unproductive desert and, given the lack of artificial irrigation systems, changing present-day warmhouse into a cooling cycle might be economically catastrophic for the region.

View Article: PubMed Central - PubMed

Affiliation: CONICET - Universidad Nacional de San Juan, InGeo, (5401) San Juan, Argentina.

ABSTRACT
The Paraná delta, growing at a rate of c. 2 km(2) yr(-1) since 6,000 yrs, is one of the most complete records of the Late Holocene in southern South America. The evolution of this 17,400 km(2) delta enclosed in Plata estuary, can be tracked by a series of 343 successive coastal-ridges showing a c.11 years period, in coincidence with sunspot cycle, also found in some North Hemisphere coastal-ridge successions. The Paraná delta shifted from fluvial, to wave-dominated, and back to the present fluvial-dominated delta, in response to climate changes associated with wind activity correlating with South American glacial cycles. The wave-dominated windy period coincides with the activation of the Pampean Sand Sea, suggesting desert conditions prevailed on the Pampas between 5,300 and 1,700 yrs, in coincidence with scarce or absent pre-historic aborigine remains ("archeological silence"). Further warmer and less windy conditions allowed human repopulation. Results suggest that aside the solar forcing, both short and medium term climate changes controlled delta evolution. An important learning is that a slight cooling would turn the highly productive pampas, into that unproductive desert and, given the lack of artificial irrigation systems, changing present-day warmhouse into a cooling cycle might be economically catastrophic for the region.

No MeSH data available.


Related in: MedlinePlus

Evolution of the wave-dominated delta with captions of environmental changes.(A) Plot of ridge unconformities, wind intensity (linearity), river flood intensity (ridge size) and delta front interaction with paleoislands against preferred time-frame. Ridges after #330 do not follow same time-scale. (B) Change from the fluvial-dominated delta with inter-distributary bays to a wave-dominated delta at ridge #1, (C) Convergence of younger ridges with ridge #1, and fluvial reworking. (D) Change from linear to segmented and curved ridges, showing location of 14C dating suggesting climate amelioration started at c. 2,400 yrs BP. (E) Last ridges of the continuous 330 succession, with location of published 14C dates67, marking the onset of present-day mild conditions. Scale bar is 1 km in each scene.
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f3: Evolution of the wave-dominated delta with captions of environmental changes.(A) Plot of ridge unconformities, wind intensity (linearity), river flood intensity (ridge size) and delta front interaction with paleoislands against preferred time-frame. Ridges after #330 do not follow same time-scale. (B) Change from the fluvial-dominated delta with inter-distributary bays to a wave-dominated delta at ridge #1, (C) Convergence of younger ridges with ridge #1, and fluvial reworking. (D) Change from linear to segmented and curved ridges, showing location of 14C dating suggesting climate amelioration started at c. 2,400 yrs BP. (E) Last ridges of the continuous 330 succession, with location of published 14C dates67, marking the onset of present-day mild conditions. Scale bar is 1 km in each scene.

Mentions: The first change, a switch from a fluvial-dominated to a wave-dominated delta, evidenced by the apparition of coastal-ridges occurred soon after the delta initiated. The first ridge (#1, Fig. 2A), has provided several bivalve shells (Erodona mactroides) dated by different authors by 14C yielding ages of 6,440 ± 110; 6,030 ± 140; 5,871 ± 42; 5,690 ± 170; 5,610 ± 110; 5,280 ± 100678 yrs BP. These varied ages suggest the #1 ridge is stratigraphically complex, evidenced in our mapping by the convergence of ridges #2 until #80 (Figs 1 and 2A,B) towards this same ridge. Due to the age uncertainty, and the fact many complex coastal ridges contain reworked shells of unknown age we used the youngest date (c. 5,300 yrs. BP) for determining the starting time for ridge progradation, which as discussed further is consistent with other high-resolution climate records of South America. We also used the youngest date obtained on this ridge for the time of wave-dominated delta initiation, as this ridge collected reworked shells of previously deposited units, for at least 900 years, our estimated time span between ridges #1 and #80. During the wave-dominated delta, a delta front was formed and delta-foresets were recorded by Colombo et al. (2007)10 using ground penetrating radar. The second major change is a return to a fluvial-dominated delta, determined by a rather abrupt end to this long beach-ridge succession. This change is estimated at c. 1,720 yrs BP based on two 14C dates of 1,770 ± 33 and 1,902 ± 41567, from ridges #316 and #326 respectively (Fig. 2D & 3E) located close to the last ridge (#332) of the succession. Several erosive surfaces and hiatuses are recognized along this ridge succession at both extremes of some ridge packages (Figs 2 & 3), that we interpret as the effect of changes of locus of sediment delivery point (channel mouth) resulting in transient coastal erosion. We avoided these unconformities (lack of continuity) by following the problematic ridges laterally until a point the ridge truncation disappeared. Unconformities are represented in Fig. 3, along with the variation of two ridge characteristics: linearity and size.


Climate changes and solar cycles recorded at the Holocene Paraná Delta, and their impact on human population.

Milana JP, Kröhling D - Sci Rep (2015)

Evolution of the wave-dominated delta with captions of environmental changes.(A) Plot of ridge unconformities, wind intensity (linearity), river flood intensity (ridge size) and delta front interaction with paleoislands against preferred time-frame. Ridges after #330 do not follow same time-scale. (B) Change from the fluvial-dominated delta with inter-distributary bays to a wave-dominated delta at ridge #1, (C) Convergence of younger ridges with ridge #1, and fluvial reworking. (D) Change from linear to segmented and curved ridges, showing location of 14C dating suggesting climate amelioration started at c. 2,400 yrs BP. (E) Last ridges of the continuous 330 succession, with location of published 14C dates67, marking the onset of present-day mild conditions. Scale bar is 1 km in each scene.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526942&req=5

f3: Evolution of the wave-dominated delta with captions of environmental changes.(A) Plot of ridge unconformities, wind intensity (linearity), river flood intensity (ridge size) and delta front interaction with paleoislands against preferred time-frame. Ridges after #330 do not follow same time-scale. (B) Change from the fluvial-dominated delta with inter-distributary bays to a wave-dominated delta at ridge #1, (C) Convergence of younger ridges with ridge #1, and fluvial reworking. (D) Change from linear to segmented and curved ridges, showing location of 14C dating suggesting climate amelioration started at c. 2,400 yrs BP. (E) Last ridges of the continuous 330 succession, with location of published 14C dates67, marking the onset of present-day mild conditions. Scale bar is 1 km in each scene.
Mentions: The first change, a switch from a fluvial-dominated to a wave-dominated delta, evidenced by the apparition of coastal-ridges occurred soon after the delta initiated. The first ridge (#1, Fig. 2A), has provided several bivalve shells (Erodona mactroides) dated by different authors by 14C yielding ages of 6,440 ± 110; 6,030 ± 140; 5,871 ± 42; 5,690 ± 170; 5,610 ± 110; 5,280 ± 100678 yrs BP. These varied ages suggest the #1 ridge is stratigraphically complex, evidenced in our mapping by the convergence of ridges #2 until #80 (Figs 1 and 2A,B) towards this same ridge. Due to the age uncertainty, and the fact many complex coastal ridges contain reworked shells of unknown age we used the youngest date (c. 5,300 yrs. BP) for determining the starting time for ridge progradation, which as discussed further is consistent with other high-resolution climate records of South America. We also used the youngest date obtained on this ridge for the time of wave-dominated delta initiation, as this ridge collected reworked shells of previously deposited units, for at least 900 years, our estimated time span between ridges #1 and #80. During the wave-dominated delta, a delta front was formed and delta-foresets were recorded by Colombo et al. (2007)10 using ground penetrating radar. The second major change is a return to a fluvial-dominated delta, determined by a rather abrupt end to this long beach-ridge succession. This change is estimated at c. 1,720 yrs BP based on two 14C dates of 1,770 ± 33 and 1,902 ± 41567, from ridges #316 and #326 respectively (Fig. 2D & 3E) located close to the last ridge (#332) of the succession. Several erosive surfaces and hiatuses are recognized along this ridge succession at both extremes of some ridge packages (Figs 2 & 3), that we interpret as the effect of changes of locus of sediment delivery point (channel mouth) resulting in transient coastal erosion. We avoided these unconformities (lack of continuity) by following the problematic ridges laterally until a point the ridge truncation disappeared. Unconformities are represented in Fig. 3, along with the variation of two ridge characteristics: linearity and size.

Bottom Line: The evolution of this 17,400 km(2) delta enclosed in Plata estuary, can be tracked by a series of 343 successive coastal-ridges showing a c.11 years period, in coincidence with sunspot cycle, also found in some North Hemisphere coastal-ridge successions.Results suggest that aside the solar forcing, both short and medium term climate changes controlled delta evolution.An important learning is that a slight cooling would turn the highly productive pampas, into that unproductive desert and, given the lack of artificial irrigation systems, changing present-day warmhouse into a cooling cycle might be economically catastrophic for the region.

View Article: PubMed Central - PubMed

Affiliation: CONICET - Universidad Nacional de San Juan, InGeo, (5401) San Juan, Argentina.

ABSTRACT
The Paraná delta, growing at a rate of c. 2 km(2) yr(-1) since 6,000 yrs, is one of the most complete records of the Late Holocene in southern South America. The evolution of this 17,400 km(2) delta enclosed in Plata estuary, can be tracked by a series of 343 successive coastal-ridges showing a c.11 years period, in coincidence with sunspot cycle, also found in some North Hemisphere coastal-ridge successions. The Paraná delta shifted from fluvial, to wave-dominated, and back to the present fluvial-dominated delta, in response to climate changes associated with wind activity correlating with South American glacial cycles. The wave-dominated windy period coincides with the activation of the Pampean Sand Sea, suggesting desert conditions prevailed on the Pampas between 5,300 and 1,700 yrs, in coincidence with scarce or absent pre-historic aborigine remains ("archeological silence"). Further warmer and less windy conditions allowed human repopulation. Results suggest that aside the solar forcing, both short and medium term climate changes controlled delta evolution. An important learning is that a slight cooling would turn the highly productive pampas, into that unproductive desert and, given the lack of artificial irrigation systems, changing present-day warmhouse into a cooling cycle might be economically catastrophic for the region.

No MeSH data available.


Related in: MedlinePlus