Creating an inset for a temperature graph

I have created a facet_wrap plot, showing the sea surface temperatures across time for four regions of the great barrier reef, and would like to highlight particular years (e.g. 1997-98 or 2015-15). Are there any recommendations for how best to add this to my existing code which is as follows:

library(ggplot2)
library(readxl)
library(readr)
library(dplyr)

FN <- read_csv("FINALSST.csv")

FN2 <- mutate(FN, Time2=as.Date(Time, format="%d/%m/%Y"))

FN2$Region <- factor(FN2$Region, levels=c("Far Northern", "Northern", "Central", "Southern"))

ggplot(data = FN2, aes(Time2, Value, col=Variable)) +
geom_line(size = 0.1) +
geom_point(size = 0.1) +
labs(title = "Great Barrier Reef SSTs from 1985 to 2017", y = "Sea Surface Temperature (°C)", x = "Date") +
facet_wrap(~Region, ncol=1)

I have also attached an image of the plot created as of now.