The Posthuman Reality of Feed-Based Social Media Systems

The conceptual boundary between the subject and user parallels the boundary between humanist and posthumanist definitions of human being, and the challenges of new media communications technology today impel this evolution. My dissertation discusses subjectivity as the self-differentiation of a particular set of processes, and the influence of communications media upon this process. Here, it includes the basis of differentiation for an I, including: the question of identity, potential agency, and knowledge. The collage of attributes that constitute a portrait of what I call the user, the subject of online social media, is demonstrably emergent, dispersed, and discursive; in terms of agency and sovereignty, the useras with other instances of posthuman subjectivityis contingent upon its media ecology and is decidedly less free than other definitions of subjectivity (such the self-sovereign individual of the social contract, which comes to be as a negation of contingency). The concept of self-sovereignty excludes the influences of history, and other influences upon the emergence of the subject, emphasizing an exclusively internal causation. The users existence, conversely, is processual and dispersed throughout networks; its being and agency are dividual, not individual. The subjectivity of the user must thus be thought in terms of its mediated contingency, as the self-sovereign agency that is characteristic of humanist traditions is less applicable to todays media ecologies. I argue that the traits of the subject in humanist traditions can be interpreted as the epiphenomena of societies whose information ecology was dominated by logocentric, typographic literacy. Today, with the advent of social media and its users, we can understand from a new vantage how subjectivities are modulated, amplified, and attenuated by technical distributions, particularly the unseen (and unseeable) non-human agents in the computation systems that constitute online social networks

Erosion rates and sediment flux within the Potomac River basin quantified over millennial timescales using beryllium isotopes

Beryllium isotopes measured in detrital river sediment are often used to estimate rates of landscape change at a basin scale, but results from different beryllium isotope systems have rarely been compared. Here, we report measurements of in situ and meteoric 10Be (10Bei and 10Bem, respectively) along with measurements of reactive and mineral phases of 9Be (9Bereac and 9Bemin, respectively) to infer long-term rates of landscape change in the Potomac River basin, North America. Using these data, we directly compare results from the two different 10Be isotope systems and contextualize modern sediment flux from the Potomac River basin to Chesapeake Bay. Sixty-two measurements of 10Bei in river sand show that the Potomac River basin is eroding on average at 29.6 ± 14.1 Mg km-2 yr-1 (11 ± 5.2 m m.y.-1 assuming a rock density of 2700 kg m-3)-a rate consistent with other estimates in the mid-Atlantic region. 10Bei erosion rates correlate with basin latitude, suggesting that periglacial weathering increased with proximity to the former Laurentide Ice Sheet margin. Considering the 10Bei-derived erosion rate as a sediment flux over millennia, rates of sediment delivery from the Potomac River to Chesapeake Bay are up to ~5× lower than contemporary sediment yields implying modern land-use practices have accelerated erosion and sediment transport over background rates. However, 10Bei erosion rate data suggest that regulatory benchmark levels used to manage sediment export from the Potomac River basin to Chesapeake Bay are set appropriately to reduce sedimentation and restore the Bay\u27s ecological health. The mean of 56 10Bem/9Bereac-derived denudation rates (40.0 ± 21.7 Mg km-2 yr-1) is higher than, but statistically indistinguishable from, the mean 10Bei erosion rate (29.6 ± 14.1 Mg km-2 yr-1; p = 0.003). However, when considered basin by basin, 10Bem/9Bereac-determined denudation rates are only weakly correlated (R2 = 0.208; p \u3c 0.001) with sediment fluxes determined from the well-established and widely used 10Bei technique. This suggests that the 10Bem/9Bereac technique may not reflect the same geomorphic processes as 10Bei technique, or that the 10Bem/9Bereac technique operates over different time and/or depth scales. Erosion indices (EIs, sensu Brown et al., 1988) derived from 10Bem measurements and contemporary sediment yield data range from 0.07 to 1.24; 75% of basins sampled have EIs that are \u3e 1, suggesting that 10Bem is being retained and sediment is being stored within the Potomac River basin. The Appalachian Plateau is the only physiographic province where sediment export dominates, likely as the result of ongoing relief growth in catchments draining the Appalachian Mountain divide. 10Bem concentrations measured in the 150 k.y. Hybla Valley sediment core, taken from the lower Potomac River basin, suggest that 10Bem and sediment are preferentially stored in the catchment when vegetation proxies for climate suggest warmer conditions prevailed. 10Bem and sediment are exported when vegetation proxies for climate suggest conditions are colder, perhaps a reflection of periglacial activity or changes in storm frequency and/or magnitude over glacial-interglacial cycles